Question

a number becomes double if it is increased by 10. the number is ?

Answer 1

the number is 10, because, if we add 10 to it, it becomes double i.e. 20

Answer 2

Let the number be x,
When the number is doubled, it becomes 2x.
Now according to the question,
x + 10 = 2x
= 2x - x = 10 
= x = 10

Hope that helps !!