multiplying fractions mentally. mostly, we multiply fractions in writing. however, in some cases we...
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Multiplying fractions mentallyMultiplying fractions mentally
Mostly, we multiply fractions in writing.Mostly, we multiply fractions in writing.
However, in some cases we can multiply them However, in some cases we can multiply them
mentally.mentally.
It can be useful to know how to think in such cases.It can be useful to know how to think in such cases.
Let’s investigate it...Let’s investigate it...
1st Calculate:
a) 3 × =12__ 3 times half of something = 1
12__
=12__ +
12__ +
12__ =
32__ = 1
12__
1st Calculate:
a) 3 × =12__
b) × 3 =12__
We are interested not only about result,but also how to imagine what happens in this example!
3 times half of something = 112__
1st Calculate:
a) 3 × =12__
b) × 3 =12__
Let’s remember:
3 × 3 =
2 × 3 =
1 × 3 =
triple three = 9
?double three = 6
?single three = 3
× 3 =12__
Continue the sequence!
half three = 112__
half three = 112__
3 times half of something = 112__
1st Calculate:
a) 3 × =12__
b) × 3 =12__
3 times half of something = 112__
half three = 112__
1st Calculate:
a) 3 × =12__
b) × 3 =12__
3 times half of something = 112__
half three = 112__
1st Calculate:
a) 3 × =12__
b) × 3 =12__
= of 3 =12__ 1
12__
First number tells ushow many times to take second number.
If the first number is fraction,then imagine "of" instead of "times"!
REMEMBER IT!
3 times half of something = 112__
half three = 112__
1st Calculate:
c) × 6 =12__ half of 6 = 3
1st Calculate:
c) × 6 =12__
d) 6 × =12__ 6 times half of something = 3
=62__ =
12__ +
12__ =+
12__ +
12__ +
12__+
12__ 3
half of 6 = 3
1st Calculate:
e) × 6 =13__ of 6 =1
3__ 2
1st Calculate:
e) × 6 =13__ of 6 =1
3__ 2
f) 6 × =13__ 6 times of something
13__
= 2
1st Calculate:
g) × 6 =23__ of 6 =2
3__ 4
Calculation: 6 ÷ 3 × 2
÷
×
= 4
1st Calculate:
g) × 6 =23__
h) 6 × =23__ 6 times of something
23__
= 4
of 6 =23__ 4
1st Calculate:
i) × 21 =27__ of 21 =2
7__ 6
Calculation :
÷
×
21 ÷ 7 × 2 = 6
1st Calculate:
j) × 36 =59__ of 36 =5
9__ 20
Calculation :
÷
×
36 ÷ 9 × 5 = 20
1st Calculate:
k) × 24 =23__ of 24 =2
3__ 16
Calculation :
÷
×
24 ÷ 3 × 2 = 16
1st Calculate:
l) 4 × =12__ 4 times half of something = 2
m) × 4 =12__ of 4 1
2__ = 2
2nd Calculate:
a) 2 × 3 =12__ 2 times 3 and a half of something = 7
2nd Calculate:
a) 2 × 3 =12__ 2 times 3 and a half of something = 7
2nd Calculate:
a) 2 × 3 =12__
b) 3 × 2 =12__ 3 and a half times 2 breads = 7
6 1+ = 7
2 times 3 and a half of something = 7
2nd Calculate:
a) 2 × 3 =12__
b) 3 × 2 =12__
6 1+ = 7
3 and a half times 2 breads = 7
2 times 3 and a half of something = 7
2nd Calculate:
a) 2 × 3 =12__
b) 3 × 2 =12__
6 1+ = 7
6 1+ = 7
3 and a half times 2 breads = 7
2 times 3 and a half of something = 7
2nd Calculate:
c) 4 × 6 =12__ 4 times 6 and a half of something = 26
24 2+ = 26
2nd Calculate:
c) 4 × 6 =12__
d) 6 × 4 =12__ 6 and a half times 4 strawberries = 26
24 2+ = 26
4 times 6 and a half of something = 26
2nd Calculate:
e) 8 × 6 =12__
48 4+ = 52
Calculate mentaly…
52
2nd Calculate:
e) 8 × 6 =12__
52
f) 4 × 10 =12__
40 5+ = 45
45
2nd Calculate:
e) 8 × 6 =12__
52
f) 4 × 10 =12__ 45
g) 5 × 4 =12__
20 + 212__
= 2212__
2212__
2nd Calculate:
e) 8 × 6 =12__
52
f) 4 × 10 =12__ 45
g) 5 × 4 =12__ 22
12__
h) 3 × 9 =12__
Say just the solution...
3112__
2nd Calculate:
e) 8 × 6 =12__
52
f) 4 × 10 =12__ 45
g) 5 × 4 =12__ 22
12__
h) 3 × 9 =12__ 31
12__
i) × 15 =12__ 7
12__
2nd Calculate:
j) × 10 =12__ 5
k) × 19 =12__ 9
12__
l) × 100 =12__ 50
m) × 101 =12__ 50
12__
n) × 102 =12__ 51
o) 1 × 7 =12__ 10
12__
p) × 56 =27__ 16
Is it enough?
T H E E N D
With thanks to:
Rex BoggsRex Boggsfor support and help with the translation into fluent U.S. idiom (a.k.a. ‘American’).
Author of presentation:
Antonija HorvatekAntonija HorvatekCroatia , January 2014
You are welcome to use this presentation in your teaching.Additionally, you can change some parts of it if used solely for teaching.
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Antonija Horvatekhttp://www.antonija-horvatek.from.hr/ [email protected]