The denominator are the same 5 and 5, why is that important? Because if you don’t have them the same they are totally different numbers. 1/10 is 10/100 and 1/5 is 20/100. In the picture everything’s working the denominator are the same and billy spends 2$ out of his 5$ at the candy store and he  spends 1$ out of his 5$ at the dollar store he needs to find out how much he spent. 2/5+1/5 =3/5, he spent 60% of his money.