Question

If 8 times a number is decreased by 20,the result is the same as 3 times the number increased by 80

Answer 1

Let the number = x, then you can easily convert the sentence into math/algebra:

If 8 times a number is decreased by 20, the result is the same as 3 times the number increased by 80
8x - 20 = 3x + 80

There, now we can solve for x.
8x - 20 = 3x + 80
5x = 100
x = 20

The number, x, is 20