The phone company charges 10 cents to connect a call for one minute and 8 cents per minute after that. How long could you talk on the phone for 1 dollar?

The phone company charges 10 cents to connect a call for one minute and 8 cents per minute after that.

We call x minute to talk after the first minute.

We have 10+8x ≤100 (cents)

and 8x≤100-10

or 8x≤90 and x≤90:8

and x≤11.25

So: How long could you talk on the phone for 1 dollar: it is 11 minute and 15 seconds