If I had one more sister I would have twice as many sisters as brothers. If I had one more brother I would have the same number of each. How many brothers and sisters do I have?

Answer

Three sisters and two brothers.

This can be solved by simple deduction, but if algebra is used let x be the number of sisters and y the number of brothers:

x+ 1= 2y

y+ 1= x

Therefore, y + 1+ 1= 2y

so y =2 or x + 1= 2x – 2

so x = 3.