Page 29 - General_Knowledge_7

Mathemagic

Multiplying By 125:

A. Multiplying by 125 is easy, if you know that 125 = 1000 ÷ 8. So, to multiply by 125, you should
divide by 8 and use the following rules on the remainder (n MOD 8):

1. If (n MOD 8) = 0 then write 000.

2. If (n MOD 8) = 1 then wri te 125.

3. If (n MOD 8) = 2 then write 250.

4. If (n MOD 8) = 3 then write 375. *Notice this is (125 × r), where r is the remainder.

5. If (n MOD 8) = 4 then write 500.

6. If (n MOD 8) = 5 then write 625.

7. If (n MOD 8) = 6 then write 750.

8. If (n MOD 8) = 7 then write 875.

B. Examples:

Ex [1] 125 x 26 =_________.
a) 26 ÷ 8 = 3 with a remainder of 2. Write 3.

b) By (3.) we write 250.
c) The answer is 3250.

Ex [2] 487 x 125 =_________.
a) 487 ÷ 8 = 60 with a remainder of 7. Write 60.

b) By (8.) we write 875.
c) The answer is 60875.

C. Try some yourself :

a. 125 × 12 = .

b. 125 × 72 = .

c. 125 × 23 = .

d. 125 × 40 = .

e. 125 × 9 = .

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