MULTIPLYING BY 5, 50, 25 ...

MULTIPLYING BY 5

The numbers 2 and 5 are closely related because 2 × 5 = 10 and 10 is a base number.
We can multiply by 5 means  multiplying by 10  it means add one zero  and halving the result.
Find 44 × 5.
44 × 10 = 440
We find half of 440, which is 220.
 So 44 × 5 = 220.

MULTIPLYING BY 50

The numbers 2 and 50 are closely related because 2 × 50 = 100 and 100 is a base number.now we can use the same trick with 50
Find 87 × 50
87 × 100=8700
Half of 8700 is 4350. So 87 × 50 = 4350.

MULTIPLYING BY 25 

The numbers 4 and 25 are closely related because 4 × 25 = 100 and 100 is a base number.
now we can use the same trick with 25
Find 82 × 25.
 25 is half of half of 100, so to multiply a number by 25 we multiply it by 100 and halve twice. So we find half of half of 8200,
82 × 100= 8200
half of 8200 is 4100
half of 4100 is 2050
 which is 2050.
 82 × 25 = 2050. 

Similarly we can  easily use  this trick for decimal
 5.2 × 50 = half of 520 = 260
The same trick you can use for  the base 1000, 10000,100000..we can simply multiply any number with 250 ,500, 5000..

  Practice 

a 46 × 50   b 864 × 50   c 72 × 25   d 85 × 25   e 86.8 × 50   f 4.2 × 50   g 34.56 × 50   h 2.8 × 25i 68 × 5   j 42 × 5   k 36 × 5   l 426 × 5   m 8.6 × 5   n 5.4 × 5   o  4.68 × 5   p 0.66 × 5