Answer:
$34
Step-by-step explanation:
I'd work backwards.
For the third book, she paid all her remaining money. The problem says she paid "1/2 her leftover money + $3". This means that: (let m = money used to buy book 3)
m = 1/2m + 3
1/2m = 3
m = 6
For the second book: (let n = money before book 2)
n - m (money left after book 2) = 1/2n + 2
1/2n +2 is money used up for book, which is the same as n-m.
n = 1/2n + 2 + m
1/2n = 2 + m = 2 + 6
1/2n =8
n = 16
For the first book, she spent 1/2 her money + 1. If o = money before book 1 (or the whole allowance):
o - n = 1/2o + 1
o = 1/2o + n + 1 = 1/2o + 16 + 1
1/2o = 17
o = 34
Check!
Spent 17 (half 34) + 1 on book 1
16 left
Spent 8 (half 16) +2 on book 2
6 left
Spent 3 (half 6) + 3 on book 3
0 left
