Aside from using a calculator, what is a quick way to get the product of a # ending in 5 multiplied by itself?

Answer 1

Here's how to do it:
1. The last 2 digits are always 25.
2. To get the leftmost number or numbers: add 1 to the leftmost number you're multiplying and multiply it by itself.

So:
15 x 15 = 225 (first digit is 1 x 2; last 2 digits are 25)
25 x 25 = 625 (first digit is 2 x 3; last 2 digits are 25)
35 x 35 = 1225 (3 x 4 are the first 2 digits; 25 is the last 2 digits)

Answer 2

Say the no is A5

Then A5
A5
-----------------
Ax(A+1)25

eg
45
45
--------
2045 4x (4+1) =20, 5x5 =25


I have a better thing for you, a trick which with little practice helps you multiply any number with any number.

Suppose you multiply ABC with EFG, then the formula is
AB
EF
----------
|X|

Which means

Multiply B with F and wright down the result in extreme right.
Then Multiply A with F and add to it the product of E and B the result goes in the middle.
Multiply A with E and wright down the result in extreme left.

Eg.

34
76
-----------
4 6x4= 24, wright 4 carry 2
84 3x6 +7x4 + 2= 18+28+2=48 wright 8 carry 4
2584 3x7+4=25

if you extrapolate this you can multi ply any no with any no. in a single line.

Answer 3

pencil and paper