A textbooks store sold a combined total of 233 biology and chemistry textbooks in a week. The number of chemistry textbooks sold was 65 less than the number of biology textbooks sold. How many textbooks of each type were sold?

Answer: Number of biology textbooks is 149

Number of chemistry textbooks is 84

Step-by-step explanation:

Let x = the number of biology textbooks sold in the week.

Let y = the number of chemistry textbooks sold in the week

The textbooks store sold a combined total of 233 biology and chemistry textbooks in a week. This means that

x + y = 233

The number of chemistry textbooks sold was 65 less than the number of biology textbooks sold. This means that

x = y + 65

Substituting x = y + 65 into x + y = 233, it becomes

y + 65 + y = 233

2y = 233 - 65 = 168

y = 168/2 = 84

x = y + 65

x = 84 + 65 = 149