Expert: Lynn Houston - 2/17/2009

Question
betty has 100 dollars more than bob.after spending 20 dollars betty has 5 times more than bob. how much does bob have. my answer is 20 dollars, but i dont know the written formula. can you help

Answer
Let's say betty has x dollar and Bob has y dollars.  Therefore,
y+100=x

If betty spends $20 (x-20) she has 5 times more than bob, so
x-20 = 5y

Use the value of x in the first eq to solve the second eq.

y+100 - 20 = 5y
80 = 4y
y = 20, therefore x = 120