SOLUTION: My daughter was given this math problem today and i would like to teach her how to do it....but don't know how! Janet spent 100.00 on books. This was K dollars less than five t

Question 565114: My daughter was given this math problem today and i would like to teach her how to do it....but don't know how!
Janet spent 100.00 on books. This was K dollars less than five times what she spent on lunch. How much did she spend on lunch?
What I got was: 5x-k=100
5x=100+k
x=100+k/5
But that does not give her an answer and she thinks I'm crazy!!!
Answer by KMST(5328) (Show Source): You can put this solution on YOUR website!
Puzzling. I can make a few guesses, but they may all be wrong.
Unless that K was misprinted or misread, there would be an infinite number of answers. Even if we say that K and the price of lunch are a whole number of dollars, there is still an infinite number of answers. Just finding two different possibilities proves that there is not enough information to solve the problem. Janet could have spent $21 on lunch and K would be $5. Janet could be very rich, and could have spent $100 or more on lunch, making K=$400 or more.
If this is grade 4-7, and the problem is exactly as posted, the expected answer may be "there is not enough information." My local school started giving that kind of problem to 4th graders in 1991. They were also supposed to figure out, and state it, if there was superfluous data, not needed to solve the problem.
If this is algebra 2, they may expect the answer as a function:
or equivalent forms or
They may expect students to say that x is a linear function of K. With integer values for K, that would be an arithmetic sequence.
WARNING:
If you are typing an answer in one line x=(100+K)/5= , but
x=100+k/5= would be incorrect
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