A textbook store sold a combined total of 356 biology and psychology textbooks in a week. The number of biology textbooks sold was three times the number of psychology textbooks sold. How many textbooks of each type were sold?

We can use the equation: x+3x=356

x=89

Since the number of biology textbooks are triple the amount of psychology textbooks, we can multiple 3*89 to get the amount of biology textbooks.

3*89=267

There were 267 biology textbooks sold, and 89 psychology textbooks sold.

I hope this helps!