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A textbook store sold a combined total of chemistry and physics textbooks in a week.
The number of chemistry textbooks sold was three times the number of physics textbooks sold.
How many textbooks of each type were sold?

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Beth L. | Patient, Knowledgeable and Very Qualified Mathematics TutorPatient, Knowledgeable and Very Qualifie...
The question doesn't ask for a dollar amount per text or the dollar amounts earned (since we also don't know what they cost per book for the bookstore or how much profit they make on each book), just the amount of texts sold: (don't try to add items into the solution of a problem for something the problem doesn't ask for in the first place).

Besides, Total dollars earned divided by 4x DOES NOT EQUAL number of physics texts sold. T/4x would be the total profit from number of physics and chemistry books sold, since 4x is the total number of BOTH types of texts sold.

x = number of physics texts sold
3x = number of chemistry texts sold
4x (3x + x) = total physics and chemistry texts sold.

Without the toal number of texts sold, or the number of physics or chemistry books sold, you can only say the above. You CAN NOT tell from the information given how many physics or chemistry texts were sold unless there is a number somewhere in the problem.
Parviz F. | Mathematics professor at Community CollegesMathematics professor at Community Colle...
4.8 4.8 (4 lesson ratings) (4)
 Again here comes word problem.
   Choose a variable for unknown,
     X = Number of Physic text book sold
    3X = Number of Chemistry text sold
     X + 3X = 4x  Total number of text sold
    T = total dollar earned - Should be given as Number of $dollars in the problem.
     T/ 4X = Number of Physics text sold
     3XT / 4 = Number of Chemistry Text Sold