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 $8.10?	Pick one:
A) 426
B) 430
C) 443
D) 520
E) 486
I think first we should see in what group envelopes value less, so that we can buy as many as we can with a specific amount of money:   -the 100 pack costs 1.5$, 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 8.1$, we can buy as many as 5 packs of 100 (5 x 1.5$ = 7.5$). We then have 0.6 $ left. so we buy 20 individual envelopes. If we add up the numbers, we get   500+20= 
<gadget id="calculator">  500+20</gadget>
<output>520</output>
520 envelopes. Answer 520
<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 $8.10?