I interpreted this question wrong. Maybe I was over thinking it but the question asked how many single apples need to be purchased the ENSURE that the total number of apples is divisible by 5. So my logic was as follows:
If she bought:
1 bundle of 4 she would need to buy a single apple.
2 bundles, 2 single apples.
3 bundles, 3 single apples.
4 bundles, 4 single apples.
So if she buys 4 single apples, no matter how many bundles she purchases she can always make the total number of apples divisible by 5 even if she has to throw 3 or more away.
To me the word ensure means that she would buy as many single apples as needed, to make certain, that however many bundles she bought, she will have a total that is divisible my 5.
I even considered the OA but thought that it was too simple of an answer. To ensure that the total number of apples is divisible by 5 just make sure that the number of bundles is a multiple of 5.
