Question bank / Linear equations in one variable

Math · AlgebraMedium

A phone plan costs $35\$35 per month, which includes 200200 text messages. Each text message beyond the first 200200 costs $0.10\$0.10, and there are no other charges. One month, Dev's bill was $51.40\$51.40. How many text messages did Dev send that month?

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Answer: 364

Let tt be the number of text messages. Dev paid for t−200t - 200 extra messages, so 35+0.10(t−200)=51.4035 + 0.10(t - 200) = 51.40. Then 0.10(t−200)=16.400.10(t - 200) = 16.40, so t−200=164t - 200 = 164 and t=364t = 364.

Stopping at 164164 gives only the messages beyond the first 200200, not the total number Dev sent.

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