Final answer:
The price of an exercise book is $110. This was determined by setting up an equation where the cost of 4 books minus $80 equaled the amount of money Ann originally had, and the cost of 3 books plus $30 equaled the same amount.
Step-by-step explanation:
The student's question is to determine the price of an exercise book given the information about Ann's purchase. When Ann planned to buy 4 books but was $80 short, it implies that she had a certain amount of money which was $80 less than the total cost of 4 books. We'll call this original sum of money 'X'. If Ann was able to buy 3 exercise books and then had $30 remaining, it indicates that the cost of 3 exercise books is equal to 'X - $30'.
Here's the step-by-step explanation:
- Let the price of one exercise book be 'P' dollars.
- Therefore, 4 exercise books would cost 4P dollars.
- Ann was $80 short for 4 books, so she had X = 4P - $80.
- Ann bought 3 books, so the cost of 3 books is 3P dollars.
- With 3 books bought, she had $30 left, so X - $30 = 3P.
- Substitute X in the equation from step 3: (4P - $80) - $30 = 3P.
- Now simplify: 4P - $110 = 3P.
- Subtract 3P from both sides: P = $110.
Therefore, the price of an exercise book is $110.