Question

Ed has 100 more dollars than robert. after ed spends 20 dollars on groceries, he now has 5 times as much money as robert. how much money does robert have. the answer the book has is 20

Answer 1

Let x=amount that Robert has
Then Ed has x+100
So, our equation to solve is:
(x+100)-20=5x get rid of parens
x+100-20=5x
x+80=5x subtract x from each side
x-x+80=5x-x collect like terms
80=4x divide each side by 4
x=20 dollars-------------------amount that Robert has
x+100=20+100=120 dollars ----amount that Ed has


CK
120-20=5*20
100=100