prime number problem?

Question

here is a problem with solution.
http://docs.google.com/Doc?id=dc83hzcs_262dbzhxw

i have some doubts in the solution.

can you please clarify ?

Answer 1

There are four possible digits for the ones column. Namely 1,3,7 and 9. Since the boy is purchasing 4 items and no digit can be used twice, all of these numbers must be used once. Since 7 has to be used, One of the prices must end in 7. There are only two choices for this number, 47 and 67. It is already given that 61 was one of the prices. So, the digit 6 can't be used again. That leaves only 47.

Answer 2

I see your point. For example, if the second no. is 83, then 47 can be the third and the 4th 29. I think that works.
I guess they just picked one possibility and showed why it worked.
And there might be other possibilities.