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(*) Squaring A Number Ending In 5:
A. Squaring a number ending
in 5 is very easy. The method comes
from algebra:
(10a + 5)2
= 100(a)(a + 1) + 25
B. Using numbers instead of
variables we get the following:
1.
Write down 25.
2.
Multiply the number in the ten’s digit by that number plus 1. Write
this number down.
Ex [1] 352 =_________.
a)
Write 25.
b)
3 x (3 + 1) = 3 x 4 = 12. Write
12.
c)
The answer is 1225.
Ex
[2] 1152 =_________.
a)
Think of 11 as being the number in the ten’s digit.
b)
Write 25.
c)
11 x (11 + 1) = 11 x 12 = 132. Write
132. See Multiplying
by 11.
d)
The answer is 13225.
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