DOUBLING AND HALVING TOGETHER

DOUBLING AND HALVING TOGETHER

Sometimes we can easily solve multiplication using some tricks
We can use doubling and halving together
Find 35 × 22.
We can use doubling and halving in this sum to get a much easier sum.
We double 35 and halve 22 and this gives us 70 × 11 which has the same answer as 35 × 22.
So 35 × 22 = 70 × 11 = 770.
Find 35 × 64.
 Doubling and halving gives us 70 × 32.
 So we can use On the Flag to find 32 × 7 and put a 0 on the end.
 So 35 × 64 = 70 × 32 = 2240.   

 Practice D Multiply the following: 

a 15 × 18     b 15 × 24     c 46 × 15      d 82 × 35     e 66 × 15     f 124 × 45     g 15 × 54    h 55 × 16     i 75 × 18     j 446 × 15    k 132 × 35     l 85 × 18