I visited the pet store last week and found two kinds of pets for sale: rabbits for $5 and parakeets for $9. If I had $14 to spend, I could buy one rabbit and one parakeet. If I had $24 to spend, I could buy three rabbits ($15) and one parakeet ($9), which would amount to exactly $24. However, if I had $13 to spend, no combination of rabbits and parakeets would cost $13. Assuming that money is no concern, what is the largest amount of money that I could have and not be able to spend all of it on some combination of rabbits and parakeets?

$31

Explanation:

Starting from number 25, number 26 is a possibility, but then you get number 31 which is larger. Then the following numbers all show a possible combination:

N°        9's                 5's

25       0                    5

26

27       3                    0

28       2                    2

29       1                     4

30       0                    6

31        -                    -

32       3                   1

33       2                   3

34       1                    5

35       0                   7

36       4                   0

37       3                   2

38       2                   4

39       1                   6

40       0                  8

41        4                  1

42       3                  3

43       2                  5

44       1                   7

45       0                  9

A pattern starts to show 35-39 ; 40-44 and so on.

answer; break-even analysis;