The usual toll charge over a bridge is $1.50. If you purchase a special sticker for $10.50, the charge is $0.80. At least how many trips through the tunnel are needed before the sticker would cost less than the toll charge

Question

The usual toll charge over a bridge is $1.50.  If you purchase a special sticker for $10.50, the charge is $0.80.  At least how many trips through the tunnel are needed before the sticker would cost less than the toll charge

anonymous · Answer

x = number of times you go over the bridge
1.50x = 10.50 + .80x
1.50x - .80x = 10.50
.70x = 10.50
x = 10.50/.70
x = 15
If you went over the bridge 15 times, it would cost the same. So if you went over 16 times, then the sticker would cost less.
Lets check...
1.50(16) = 10.50 + .80(16)
24 = 10.50 + 12.80
24 = 23.30 <-- as you can see, the sticker costs less.
ANSWER : 16 times.