Question 971593
A textbook store sold a combined total of 413 psychology and math textbooks in a week. 
The number of math textbooks sold was 55 less than the number of psychology textbooks sold.
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How many textbooks of each type were sold?
Equations:
p + m = 413
m = p-55
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Substitute for "m" and solve for "p"::
p + p-55 = 413
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2p = 468
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p = 234 (# of psychology books)
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m = p-55 = 179 (# of math books)
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Cheers,
Stan H.
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