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 man has eighty-one cows ( numbered 1,2,3...81 as such). The beauty is that cow no. 1 gives 1ltr of milk, cow no. 2 gives 2ltrs of milk and so on. The man wants to equally distribute the cows among his nine sons so that each one of them gets the same quantity of milk.

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

AB * C = DE - F = GH / I

We know that the number 7 is the prime followed by a cube. Which next number is also a prime followed by a cube?

What number divided by 4 is the same as that number minus 4?

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

Find the number of squares in the below-given picture.

My grandson is about as many days as my son in weeks, and my grandson is as many months as I am in years. My grandson, my son and I together are 120 years. Can you tell me my age in years ?

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?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?