Question 206048
Tricia and Michael share a cell phone plan, together; they made a total of 52 calls last month for a total of 620 minutes. Tricia averaged 15 minutes for each of her calls, while Michael averaged 10 minutes. 
-How many calls did Tricia make last month?
 
-How many calls did Michael make last month? 

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Equations: 
Quantity Eq.::: t + m = 52
Time Eq:::::::15t + 10m = 620
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Multiply thru the 1st to set it up for elimination:
15t + 15m = 15*52
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Subtract the 2nd equation from that and solve for "m":
5m = 15*52-620
 m = 32 (# of calls Michael made)
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Substitute into t+m=52 to solve for "t":
t + 32 = 52
t = 20 (# of calls Tricia made)
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Cheers,
Stan H.