Multiply a number by 4 is doubling a number twice, i.e. you double the number 2 times (as 4 can be written as 2 x 2).
For example:
- 45 x 4 = double of (double of 45)
Double of 45 is 90, and double of 90 is 180.
So, 45 x 4 = 180
- 86 x 4 = double of (double of 86)
Double of 86 is 172, and double of 172 is 344.
So, 86 x 4 = 344
Multiply a number by 8 is doubling a number thrice, i.e. you double the number 3 times (as 8 can be written as 2 x 2 x 2)
For example:
- 45 x 8 = double of (double of (double of 45))
Double of 45 is 90, and double of 90 is 180, and double of 180 is 360.
So, 45 x 8 = 360
- 86 x 8 = double of (double of (double of 86))
Double of 86 is 172, and double of 172 is 344, and double of 344 is 688.
So, 86 x 8 = 688