Survival Guide

Seventh Grade

Math

Number Sense and Percents

Contents

Divisibility Rules Factors and Factor Pairs

Multiples Primes and Composites

Prime Factorization GCF and GCF Word Problems LCM and LCM Word Problems

Contents

Adding Mixed NumbersSubtracting Mixed Numbers Multiplying Mixed Numbers

Dividing Mixed Numbers Adding & Subtracting Decimals

Multiplying DecimalsDividing Decimals

ContentsChanging Fractions to DecimalsChanging Decimals to Fractions

Changing Fractions to PercentsChanging Percents to Fractions

Changing Decimals to PercentsChanging Percents to Decimals

The Percent Proportion

Divisibility RulesYou can always divide. These rules are

shortcuts to determine if one number divides evenly into another number.

1: All whole numbers are divisible by 12: All even numbers (numbers ending in 0, 2, 4, 6, or 8)3: The sum of the digits is divisible by 34: The number formed by the last 2 digits are divisible by 45: The number in the one’s place is a 0 or 56: The number is divisible by 2 AND 38: The number formed by the last 3 digits is divisible by 89: The sum of the digits is divisible by 910: The number in the one’s place is a 0

Divisibility RulesEXAMPLES:

162,720 is divisible by… 1, 2, 3, 4, 5, 6, 8, 9, and 101 2 (ends in a 0)3 (the sum is 1 + 6 + 2 + 7 + 2 + 0 = 18 and 18

÷ 3 = 6)4 (20 ÷ 4 = 5)5 (ends in a 0)6 (the number is divisible by 2 and 3)8 (720 ÷ 8 = 90)9 (sum is 18 and 18 ÷ 9 = 2)10 (ends in a 0)

Divisibility RulesEXAMPLES:

32,592,165 is divisible by… 1, 3, and 51 not 2 (ends in a 5)3 (the sum is 3+2+5+9+2+1+6+5 = 33 and 33

÷ 3 = 11)not 4 (4 does not divide evenly into an odd

number)5 (ends in a 5)not 6 (the number is divisible by 3 but not 2)not 8 (8 does not divide evenly into an odd

number)not 9 (sum is 33 and 33 ÷ 9 is not a whole

number)not 10 (does not end in a 0)

Divisibility RulesEXAMPLES:

745,168 is divisible by… 1, 2, 3, 4, and 81 2 (ends in a 8)3 (the sum is 7+4+5+1+6+8 = 31 and 31 ÷ 3

does not equal a whole number)4 (68 ÷ 4 = 17)not 5 (does not end in a 0 or 5)not 6 (the number is divisible by 2 but not 3)8 (168 ÷ 8 = 21)not 9 (sum is 31 and 31 ÷ 9 is not a whole

number)not 10 (does not end in a 0)

Factors and Factor Pairs

Factors are numbers you multiply together to get a product. 2 and 5 are factors of 10 because 2 x 5 = 10

A number can have many factors. The factors of 12 are 1, 2, 3, 4, 6, and 12 because 1 x 12 = 12, 2 x 6 = 12, and 3 x 4 = 12.

Factor pairs are the two numbers used to get the product.

There are 3 factor pairs for 18: 1 and 18, 2 and 9, 3 and 6. There are 4 factor pairs for 40: 1 and 40, 2 and 20, 4 and 10,

5 and 8. There is one factor pair for 11: 1 and 11

Multiples

The multiples of a number are the product of the number and any other number.

If you list the multiples of a number, the list is endless.

The first multiple of 3 is 3 because 3 x 1 = 3. The second multiple of 3 is 6 because 3 x 2 = 6. The third multiple of 3 is 9 because 3 x 3 = 9.The fourth multiple of 3 is 12 because 3 x 4 = 12.The tenth multiple of 3 is 30 because 3 x 10 = 30.The seventy-fifth multiple of 3 is 225 because 3 x 75 = 225.

Primes and CompositesPrime numbers have exactly two factors (1 and itself).

Composite numbers have three or more factors. Number Factors Prime or Composite

1 1 Neither2 1, 2 Prime3 1, 3 Prime4 1, 2, 4 Composite5 1, 5 Prime6 1, 2, 3, 6 Composite7 1, 7 Prime8 1, 2, 4, 8 Composite9 1, 3, 9 Composite10 1, 2, 5, 10 Composite11 1, 11 Prime12 1, 2, 3, 4, 6, 12 Composite

Primes and Composites

Prime numbers are white. Composite numbers are yellow. One is neither prime nor composite!!

Prime Factorization Every number has a unique prime factorization. When a number is written as a product of prime numbers, it is called the prime factorization for that number.

The prime factorization for 12 is 2 x 2 x 3 and the prime factorization for 50 is 2 x 5 x 5. Always write the prime numbers from least to greatest.

Two common methods for finding the prime factorization is a factor tree and prime division.

These two diagramsshow how to find theprime factorization for80 using both commonmethods.

Greatest Common Factor

All natural numbers share a common factor of 1. Many numbers share other factors in common.

The factors of 24 are 1, 2, 3, 4, 6, 8, 12, and 24.The factors of 36 are 1, 2, 3, 4, 6, 9, 12, 18, and 36.

The common factors are 1, 2, 3, 4, 6 and 12. The greatest common factor (GCF) is 12. It is the largest factor the numbers have in common.

The list method, used above, works well for determining the GCF of smaller numbers. For larger numbers, other methods, such as “the slide” and prime factorization are useful.

Greatest Common Factor The SLIDE Method Prime Factorization

Method

The GCF can be found The numbers in the prime by multiplying the 2 and factorization that 40 and 72 the 4. The GCF of 40 and have in common are 2 x 2 72 is 8. x 2. The GCF is 8.

Greatest Common Factor The SLIDE Method Prime Factorization Method

The GCF can be found The numbers in the prime by multiplying 4 x 3 x 10. factorization that 120 and 360 The GCF of 120 and 360 is have in common are 2 x 2 x 2 120. x 3 x 5 = 120. The GCF is 120.

GCF Word Problems

Greatest common factor word problems usually contain one of the following words in the question…greatest, most, largest, maximum, highest.

1. Juliana is putting together first-aid kits. She has 20 large bandages and 8 small bandages, and she wants each kit to be identical, with no bandages left over. What is the greatest number of first-aid kits Juliana could put together?

2. A florist has 5 tulips and 15 carnations. If the florist wants to create identical bouquets without any leftover flowers, what is the maximum number of bouquets the florist can make?

Least Common MultipleAll numbers have common multiples. It is often helpful to find the least common multiple (also known as the least common denominator) when adding and subtracting fractions.

The first 10 multiples of 6 are 6, 12, 18, 24, 30, 36, 42, 48, 54, 60.The first 10 multiples of 8 are 8, 16, 24, 32, 40, 48, 56, 64, 72, 80.

The common multiples in the list are 24 and 48. The least common multiple (LMC) of 6 and 8 is 24. It is the smallest multiple the two numbers have in common.

The list method, used above, works well for determining the LCM of smaller numbers. For larger numbers, other methods, such as “the slide” and prime factorization are useful.

Least Common Multiple The SLIDE Method Prime Factorization Method

The LCM can be found To find the LCM, multiply the by multiplying the 2, 4, numbers they have in common 5 and 9. The LCM of 40 (the 2 x 2 x 2) with the numbers and 72 is 360. not in common (3 x 3 x 5). The

LCM of 40 and 72 is 360.

Least Common Multiple The SLIDE Method Prime Factorization Method

The LCM can be found To find the LCM, multiply the by multiplying the 2, 7, number they have in common and 8. The LCM of 14 (the 2) with the numbers not and 16 is 2 x 7 x 8 = 112. in common (2 x 2 x 2 x 7). The

LCM of 14 and 16 is 112.

LCM Word Problems

Least common multiple word problems usually contain one of the following words in the question…least, smallest, minimum.

1. Sara's Bath Shop sells bars of soap in boxes of 2 bars and bottles of soap in boxes of 19 bottles. An employee is surprised to discover that the shop sold the same number of bars and bottles last week. What is the smallest number of each type of soap that the shop could have sold?

2. Butler Stationery sells cards in packs of 18 and envelopes in packs of 16. If Evan wants the same number of each, what is the least number of cards that he will have to buy?

LCM Word ProblemsA second type of least common multiple word problem will have two or more things happening over and over again. The question will want to know when those things will happen again at the same time.

1. Jordan rides his bike every 3 days, swims every 2 days, and runs every 4 days. If he did all three exercises today, in how many days will he do all three again on the same day?

2. Maria cleans her over every 40 days and washes windows every 50 days. If she did both chores today, in how many days will she do both chores again on the same day?

Adding Mixed Numbers

1. Find the least common denominator (LCD). For this problem, the LCD is 20.

2. Rewrite the problem with equivalent fractions using the LCD.

3. Add the numerators. 4. Keep the denominator.5. Add the whole numbers.6. Finalize the problem by making sure the fraction is not improper. Always simplify!

Subtracting Mixed Numbers

1. Find the least common denominator (LCD). For this problem, the LCD is 20.

2. Rewrite the problem with equivalent fractions using

the LCD.3. Subtract the numerators. 4. Keep the denominator.5. Subtract the whole numbers.6. Always simplify!

Subtracting Mixed Numbers

In this problem, you must rename (also known as borrow) before you can subtract the numerators.

To rename a mixed number, subtract 1 from the whole number and add it to the fractional part. Change the

fractional part to an improper fraction.

Multiplying Mixed Numbers

1. Rewrite every mixed number as an improper fraction.

2. Optional: Cross-cancel and reduce fractions to make the next steps easier!

3. Multiply the numerators straight across.4. Multiply the denominators straight across.5. If the answer is improper, change it to a mixed

number.6. Always simplify!

Dividing Mixed Numbers1. Rewrite every mixed number as an improper

fraction.2. Multiply by the reciprocal. This means change the

divide sign to multiply and “flip” the fraction that came after divide sign.

3. Optional: Cross-cancel and reduce fractions to make the next steps easier!

4. Multiply the numerators straight across.5. Multiply the denominators straight across.6. If the answer is improper, change it to a mixed

number.7. Always simplify!

Adding & Subtracting Decimals

1. Line up the decimal points!2. Add zeros after the decimal points, if needed.3. Bring the decimal point straight down.4. Add or subtract.

Multiplying Decimals

1. Line up the last digit of each number. There is no need to line up the decimals.

2. Multiply the numbers as if they are whole numbers. Ignore the decimals for now.

3. After multiplying, determine where the decimal should be placed. Count the number of digits after the decimal point for both factors. Your answer needs to have the same number of digits after the decimal point.

In this first example, there are threedigits after the decimal point (3, 2, 7).As a result, the answer has three

digits after the decimal point (0, 2, 4).

Dividing by Whole Numbers

When dividing by a whole number,remember to repeat the followingsteps: divide, multiply, subtract, andbring down the next number.

When you reach the end of the wholenumber, you are no longer to write theleftover number as a remainder!

Instead, add a decimal and bring itup to the answer. Then add as manyzeros as you need to keep dividing.

In some cases, as the second example,you will begin to notice a repeatingpattern. Use a bar over the repeatingnumbers.

REMEMBER TO KEEP ALL YOUR NUMBERS AND DECIMALS LINED UP!!

Dividing by Decimals

When dividing by a decimal, you must FIRST make the divisor into a whole number. This is done by moving the decimal to the right. Then count the number of places you moved the decimal point and do the exact same thing to the dividend. The dividend does NOT need to be a whole number!

Notice in the first example, when the decimal is moved once in the divisor, it is moved once in the dividend. In the second example, when the decimal is moved twice in the divisor, it is moved twice in the dividend. Zeros are added as needed.

REMEMBER TO KEEP ALL YOUR NUMBERS AND DECIMALS LINED UP!!

Changing Fractions to Decimals

Many fractions can be changed to decimals by using place value. Here are a few examples:• is equal to . Six tenths is 0.6 as a decimal.

• is equal to which is 0.28 as a decimal.

When this does not work, remember that a fraction is just another way to write a

division problem. • is equal to 1 ÷ 8 which equals 0.125

• is equal to 7 ÷ 12 which equals 0.58

Changing Decimals to Fractions

Changing decimals to fractions is as easy as reading the number! Remember to simplify the fraction.• 0.32 is thirty-two hundredths = = • 0.9 is nine tenths = • 0.012 is twelve thousandths = = • 0.145 is one hundred forty-five

thousandths = =

Changing Decimals to PercentsTo change a decimal to a percent, move the decimal two places to the right and add a percent sign.

0.57 = 57% 0.29 = 29%

0.5 = 50% 0.06 = 6%

0.002 = 0.2% 1.05 = 105%

Changing Percents to DecimalsTo change a percent to a decimal, move the decimal two places to the left and remove the percent sign.

36% = 0.36 45% = 0.45

70% = 0.70 = 0.7 8% = 0.8

1.9% = 0.019 435% = 4.35

Changing Percents to Fractions

Percent means per hundred. Every percent can be changed into a fraction by placing the percent over 100. Remember to simplify.Examples: 68% = = 115% = = 1 = 1

If the percent contains a decimal, a little more work is required. Change the percent to a decimal and then to a fraction.Examples: 37.5% = 0.375 = = Examples: 5.25% = 0.0525 = =

Changing Fractions to Percents

Percent means per hundred. If you can write an equivalent fraction with a denominator of 100, the numerator is the percent.Examples: so = 48%

so = 12%When this doesn’t work, change the fraction to a decimal by dividing and then change the decimal to a percent. Examples: = 19 ÷ 32 = 0.59375 = 59.375%

Percent Problems: The % Proportion

The Percent Proportion is = .Examples: What percent of 50 is 30? = Answer: 60%

32 is 40% of what number? = Answer: 80

75% of 420 is what number? = Answer: 315

115% of what number is 805? = Answer: 700

Percent Problems: The % Proportion

For story problems, this percent proportion works better: =

Example 1: 56% of the students in a class wear flip-flops. If there are 32 students, how many students were flip-flops? Since 32 students represents the whole class, the

proportion would be = . Solve to find18 students wear flip-flops.

Example 2: On a quiz, Marcy got 38 questions correct out of 40. What percent did Marcy get on the test? The

proportion = would give you an answer of 95%.