10 is a base number and we have seen that multiplying any number by 10 is very easy. We just add one 0 at the end of that number. Note that, 10 can be written as 2 x 5.

So, any number multiplied by 5 is equivalent to multiplying the number by 10 and halving the result.

For example:

32 x 5 = 32 x 10 ÷ 2

= 320 ÷ 2

= 160

Similarly, any number multiplied by 50 is equivalent to multiplying the number by 100 and halving the result. Note that, 100 = 50 x 2

For example:

42 x 50 = 42 x 100 ÷ 2

= 4200 ÷ 2

= 2100

Similarly, any number multiplied by 25 is equivalent to multiplying the number by 100 and halving the result twice. Note that, 100 = 25 x 4.

For example:

26 x 25 = 26 x 100 ÷ 4

= 2600 ÷ 4

= 650

Try these:

a 56 × 50                 b 464 × 50                   c 72 × 25                              d 85 × 25
e 46.8 × 50              f 6.4 × 50                     g 43.56 × 50                         h 2.8 × 25

i 68 × 5                    j 42 × 25                        k 36 × 50                             l 426 × 5
m 8.6 × 5                n 5.4 × 5                        o 4.68 × 5                            p 0.66 × 5