Multiplying By Twenty
Multiplying by 20 is done in two stages, by 2 and then by 10.
Multiplying By Twenty Five
To multiplying by 25:
Divide the number by 4.
If you have a remainder of 0 then add 00 at the end.
If you have a remainder of 1 then add 25 at the end.
If you have a remainder of 2 then add 50 at the end.
If you have a remainder of 3 then add 75 at the end.
Example: 143 * 25
143 / 4 = 35 remainder: 3
so
143 * 25 = 35 & 75 (for a remainder of 3 add 75 at the end)
143 * 25 = 3575
[continued]