Primary Mathematics

How to perform a quick mental calculation.

You may wonder why a person can perform a quick calculation on a number which ends with 5.
There is an unconventional way of performing such a calculation.
Let's give an example, 25 X 25 = 625 . I can provide the answer in a second the moment the question is asked. How do I do it ?
Let's folow this rule of thumb.

Look at the column on below the unit, both are 5 . When 5 X 5 , we will get 25
Let's look at the column of tenth , both are 2 . Instead of 2X2 , we shall add 1 for one of the numbers and it become 3X2 =6 .

Therefore, just combine the number 6 and 25 together , it yields 625. It sounds odd , isn't it ?
But this is true..
You coud try 35 X35 = (4X3) (5X5) = 1225

You could also try other numbers with 5 as the last number. One thing to note is that , both number has to be same.

Try it out yourselves for 45 X 45
55 X55

See it for yourselves and convince yourselves

By Loi Kheng Seong

posted by Blogs @ 6:56 AM