Question

A textbook store sold a combined total of 231 psychology and biology in a week. The number of psychology textbook sold was two times the number of biology textbook sold. How many textbook of each type were sold.

Answer 1

Psychology = 154
Biology = 77

Answer 2

Answer: the number of psychology textbook sold that week is 154.

the number of biology textbook sold that week is 77

Explanation:

Let x represent the number of psychology textbook sold in a week.

Let y represent the number of biology textbook sold in a week.

A textbook store sold a combined total of 231 psychology and biology in a week. This means that

x + y = 231 - - - - - - - - - - - - 1

The number of psychology textbook sold was two times the number of biology textbook sold. This means that

x = 2y

Substituting x = 2y into equation 1, it becomes

2y + y = 231

3y = 231

y = 231/3 = 77

Substituting y = 77 into x = 2y, it becomes

x = 2 × 77 = 154