Page 19 - General_Knowledge_7
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Mathemagic
Multiplying By 25:
A. Multiplying by 25 is one of the basic multiplication methods in number series.
1. You can rewrite 25 to be 100 ÷ 4. So the first step is to divide by 4 and write this number down.
2. Depending on the remainder, referred to as (n MOD 4), the last numbers are the following:
a) If (n MOD 4) = 0 then the last numbers are 00.
b) If (n MOD 4) = 1 then the last numbers are 25.
c) If (n MOD 4) = 2 then the last numbers are 50.
d) If (n MOD 4) = 3 then the last numbers are 75.
B. Examples:
Ex [1] 25 x 84 = .
a) 84 ÷ 4 = 21. Write 21.
b) Since there is no remainder the last numbers are 00.
c) The answer is 2100.
Ex [2] 113 x 25 = .
a) 113 ÷ 4 = 28 with a remainder of 1. Write 28.
b) The last numbers are 25.
c) The answer is 2825.
Try some yourself:
a. 76 × 25 = .
b. 41 × 25 = .
c. 16 × 25 = .
d. 110 × 25 = .
e. 62 × 25 = .
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