Envelopes can be purchased for $1.50 per pack of 100, $1.00 per pack

I think first we should see in what group envelopes value less, so that we can buy as many as we can with a specific amount of money:
-the 100 pack costs 1.5$, meaning 0.015$ per envelope
-the 50 pack costs 1$, meaning 0.02$ per envelope
-the single envelope costs 0.03$ per envelope

Thus, we have to buy as many 100 packs as we can, then as meny of 50 packs as we can and the remaining envelopes are single ones.

Having 7.3$, we can buy as many as 4 packs of 100 (4 x 1.5$ = 6$). We then have 1.3 $ left. so we buy 1 pack of 50 for 1$. We now have 0.3$ left, so we buy 10 individual envelopes. If we add up the numbers, we get 400+50+10=460 envelopes. Answer D

Solution:

We see that the cost per envelope of a pack of 100 envelopes is 1.50/100 = $0.015 and that of a pack of 50 envelopes is 1/50 = $0.02. Since the cost per envelope is the cheapest when buying a pack of 100 envelopes, we should buy as many packs of 100 envelopes first, followed by packs of 50 envelopes, and then followed by single envelopes.

Using this scheme, we can buy 4 packs of 100 envelopes, with 7.3 - 6 = $1.30 left. We then buy 1 pack of 50 envelopes, with 1.3 - 1 = $0.30 left. Finally, we can buy 10 single envelopes with the $0.30 we have left. Therefore, we can buy a maximum total of 4 x 100 + 50 + 10 = 460 envelopes.

Answer: D

I got this question right but after reading explanations i understood that i was mislead by wording. I though that three possible choice are here: to buy 100 for 1.5, 1$ per pack of 50 or pay 0.03 for each. So i tried to count the price of a single envelope. Looks like this is not correct

1 - 100 per 1.5 - we can buy 4 = 400, remaining 1.3 to spend

2 - 50 per 1 - we can buy 1 pack = 50 envelopes, remaining .3 to spend

3 - 1 per 0,3 we can buy 10 more with .3

total = 400 + 50 + 10 = 460

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