True, iffy, false 1

Pilar Chow

To multiply by 10, add an extra 0.This statement is iffy. It is true when the number This statement is iffy. It is true when the number

is a whole number.is a whole number.

10 X 10 = 100 6 X 10 = 10010 X 10 = 100 6 X 10 = 100

It is false when the number is a decimal or It is false when the number is a decimal or fractionfraction

4.8 X 10 = 48 3 X ¼ = ¾ 4.8 X 10 = 48 3 X ¼ = ¾

An even number is divisible by 2.

This statement is true. This statement is true.

2 X 98 = 1962 X 98 = 196

2 X 764 = 15282 X 764 = 1528

2 X 5 = 102 X 5 = 10

The answers above are all divisible by 2.The answers above are all divisible by 2.

Finding two fifths of a number is the same as

dividing it by 5 then multiplying by 2.

This statement is true.This statement is true.

3 X 3 X ⅖ ⅖ = 6/5= 6/5

3 ÷ 5 X 2 = 6/5 3 ÷ 5 X 2 = 6/5

2.5 X 2.5 X ⅖⅖= 1= 1

2.5 ÷ 5 X 2 = 12.5 ÷ 5 X 2 = 1

Squaring a number gives a higher number.This statement is iffy. This is because This statement is iffy. This is because

when you square “1”, it is still the when you square “1”, it is still the same. Also, when you square a same. Also, when you square a

number below 1, it gives a smaller number below 1, it gives a smaller numbernumber

0.9 0.9 squaresquare = 0.81 = 0.81

You divide a number by 2 and then by 10. The answer is

different if you divide it by 10 then by 2.

This statement is false. This is because they are both This statement is false. This is because they are both dividing by 20. dividing by 20.

6 ÷ 2 = 36 ÷ 2 = 3

3 ÷ 10 = 0.33 ÷ 10 = 0.3

6 ÷ 10 = 0.66 ÷ 10 = 0.6

0.6 ÷ 2 = 0.30.6 ÷ 2 = 0.3

The total of two numbers is greater than their difference.This statement is iffy because the total of two numbers This statement is iffy because the total of two numbers which are above zero is greater than their difference. which are above zero is greater than their difference. However the total and difference of two zeros are the However the total and difference of two zeros are the same. The total of two negative numbers is smaller same. The total of two negative numbers is smaller

than the difference.than the difference.

Negative: -1 + (- 2) = -3 -1 – (-2) = 1 -3 < 1Negative: -1 + (- 2) = -3 -1 – (-2) = 1 -3 < 1

Positive: 1 + 2 = 3 1 – 2 = -1 3 > -1Positive: 1 + 2 = 3 1 – 2 = -1 3 > -1

Zero: 0 + 0 = 0 0 – 0 = 0 0 = 0Zero: 0 + 0 = 0 0 – 0 = 0 0 = 0

If the total of two numbers is odd, so is their difference

This statement is true because: This statement is true because:

4 + 5 = 9 4 – 5 = -14 + 5 = 9 4 – 5 = -1

-3 + (-2) = -5 -3 – (-2) = -1-3 + (-2) = -5 -3 – (-2) = -1

A prime number is an odd number.

This statement is iffy because a prime number is only This statement is iffy because a prime number is only divisible by 1 or itself. An even number is always divisible by 1 or itself. An even number is always

divisible by two. So this means that only odd numbers divisible by two. So this means that only odd numbers can become prime numbers. 2 is the only even number can become prime numbers. 2 is the only even number

that is a prime number.that is a prime number.

Prime numbers up to 100: 2, 3, 5, 7, 11, 13, 17, 19, 23, Prime numbers up to 100: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83,

89, 91, 9789, 91, 97

You double a number and add 10. The answer is different if

you add 10 first and then double.This statement is false because the operations are in This statement is false because the operations are in different order. different order.

Double first (positive no.): 4 X 2 = 8 8 + 10 = 18Double first (positive no.): 4 X 2 = 8 8 + 10 = 18

Add first: 8 + 10 = 18 18 X 2 = 36Add first: 8 + 10 = 18 18 X 2 = 36

Double first (negative no.): -7 X 2 = - 14 -14 + 10 = -4Double first (negative no.): -7 X 2 = - 14 -14 + 10 = -4

Add first: -7 + 10 = 3 3 X 2 = 6 Add first: -7 + 10 = 3 3 X 2 = 6

Adding two negative numbers gives a positive number.

This statement is false. If the statement was This statement is false. If the statement was “Multiplying two negative numbers gives a “Multiplying two negative numbers gives a positive number” then it would be correct.positive number” then it would be correct.

-2 + (-2) = -4-2 + (-2) = -4

-25 + (-49) = -74-25 + (-49) = -74

-39 + (-65) = -104-39 + (-65) = -104