Find the mistake in the below maths equations

A = 2
A(A-1) = 2(A-1)
A2-A = 2A-2
A2-2A = A-2
A(A-2) = A-2
A = 1

A girl has as many brothers as sisters, but each brother has only half as many brothers as sisters. How many brothers and sisters are there in the family?

What is next number in the pattern below:

131 517 192 123 ?

How many triangles are there in the picture below?

Krish is 45 years old and his mother Crishtina is 73 years old.

Can you find out how many years ago, his mother was three times his age?

Rectify the following equality 101 - 102 = 1 by moving just one digit.

Replace each alphabet with the number (1-9) to make the below equation correct.

AB * C = DE - F = GH / I

If we add four times the age of John four years from now to five times his age five years from now we get ten times his current age.

How old will John be two years from now?

There is a square of a particular number which when doubled, becomes 7 more than its quarter.

Can you find the number?

John replied, when asked how old he was. In 2 years he will be twice as old as he was five years ago.' How old is he ?