SOLUTION: A postal clerk sold 40 stamps for $5.40. Some were 10-cent stamps and some were 15-cent stamps. How many 10-cent stamps were there?

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Question 1025835: A postal clerk sold 40 stamps for $5.40. Some were 10-cent stamps and some were 15-cent stamps. How many 10-cent stamps were there?
Found 2 solutions by ikleyn, amalm06:
Answer by ikleyn(52790) About Me  (Show Source):
You can put this solution on YOUR website!
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A postal clerk sold 40 stamps for $5.40. Some were 10-cent stamps and some were 15-cent stamps. How many 10-cent stamps were there?
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Answer by amalm06(224) About Me  (Show Source):
You can put this solution on YOUR website!
Let S1=10-cent stamps and S2=15-cent stamps
If 40 stamps cost $5.40, then 1 stamp cost 0.135
Using the method of alligation,
0.135-0.10=0.035
0.15-0.135=0.015
So that S1/S2=0.015/0.035
Then S1=(0.015/0.05)(40)=12 10-cent stamps (Answer)
S2=40-12=28 15-cent stamps (Answer)