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Question 1206099: A textbook store sold a combined total of 215 psychology and history textbooks in a week. The number of psychology textbooks sold was 57 more than the number of history textbooks sold. How many textbooks of each type were sold?
Found 4 solutions by MathLover1, mananth, ikleyn, josgarithmetic:
Answer by MathLover1(20849)   (Show Source):
Answer by mananth(16946)  (Show Source):
You can put this solution on YOUR website! A textbook store sold a combined total of 215 psychology and history textbooks in a week. The number of psychology textbooks sold was 57 more than the number of history textbooks sold. How many textbooks of each type were sold?
Psycology books sold be x
History books sold be y
store sold a combined total of 215 psychology and history textbooks in a week.
x+y=215.....................................(1)
store sold a combined total of 215 psychology and history textbooks in a week.
x=y+57
x-y=57.........................................(2)
add 1 & 2
2x = 272
x= 272/2= 136
215-136=79
79 history textbooks and 136 psychology textbooks were sold.
Answer by ikleyn(52781)  (Show Source):
You can put this solution on YOUR website! .
A textbook store sold a combined total of 215 psychology and history textbooks in a week.
The number of psychology textbooks sold was 57 more than the number of history textbooks sold.
How many textbooks of each type were sold?
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This problem can be solved MENTALLY.
Below I show you how to do it.
For a minute, from the total of 215 textbooks, take off mentally 57 psychology textbooks.
Then you will have new collection of 215-57 = 158 textbooks,
and in this updated collection, the number of psychology textbook will be the same
as the number of history textbooks.
Hence, the number of history textbook is half of 158, i.e. 158/2 = 79 textbooks.
Then the number of psychology textbook in the original collection is 79 + 57 = 136.
ANSWER. 136 psychology textbooks and 79 history textbooks.
Solved mentally, without using equations.
Answer by josgarithmetic(39617)  (Show Source):
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