Envelopes can be purchased for $1.50 per pack of 100, $1.00 per pack of 50, or $0.03 each. What is the greatest number of envelopes that can be purchased for $7.90?	Choose the correct answer
A) 426	B) 430	C) 443	D) 480	E) 486
I think first we should see in what group envelopes value less, so that we can buy as many as we can with a specific amount of money:   -the 100 pack costs 1.5$, 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 7.9$, we can buy as many as 4 packs of 100 (4 x 1.5$ = 6$). We then have 1.9 $ left. so we buy 1 pack of 50 for 1$. We now have 0.9$ left, so we buy 30 individual envelopes. If we add up the numbers, we get   400+50+30= 
<gadget id="calculator">  400+50+30</gadget>
<output>480</output>
480 envelopes. Answer 480
<result>D</result>
Envelopes can be purchased for $1.50 per pack of 100, $1.00 per pack of 50, or $0.03 each. What is the greatest number of envelopes that can be purchased for $7.90?