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
