Remember that 25 is 100/4. This means we can multiply the number by 100, and then divide by 4.

To multiply by 25, move the decimal point of the multiplicand two places to the right and divide the resulting number by 4.

Example 13.1:    Find 64 x 25

1. Since the multiplicand is a whole number, add two zeroes at the end to make it 6400.
2. Divide 6400 by 2 giving 3200
3. Divide 3200 by 2 to get the final answer, 1600

Example 13.2:    Find 9.3 x 25

1. Move the decimal point two places to the right to make it 930
2. Divide by 4 using the one line method to get 5.

 Example 13.3:    How much is $250 in pesos if the exchange rate is P45.15 = $1

1. Since 250 is one-fourth of 1000, move the decimal point three places to the right to get 45,150.
2. Divide 45,150 by 4 to get P11,287.50

 Example 13.4:    How much is the selling price of a pair of running shoes originally priced at P4,795 if it is offered at 75% discount?

A 75% discount means the selling price is just 25% or 1/4 of the original price, so the selling price is just 4,795 divided by 4 or P 1,198.75.

How about multiplying by 125?

Remember 125 is simply 1000/8.

To multiply by 125, move the decimal point three places to the left and divide the result by 8.

Example 13.5:

2 x 4 x 5 x 8 x 25 x 125 =

(2 x 5) x (4 x 25) x (8 x 125)

= 10 x 100 x 1000 = 1,000,000

Example 13.6:    384 x 125 = 384,000/8 = 48,000

Exercise 13:

1.    36 x 25 =
2.    78 x 25 =
3.    67 x 25 =
4.    256 x 125 =
5.    55 x 125 =
6.    123 x 250 =
7.    466 x 2.5 =
8.    3599 x 25% =
9.    2468 x 2.5% =
10.    2552 x 1.25% =

Answers to all exercises are found in the answer key.

Discover the 25 Math Short Cuts ( 25 MSC )!