Question 22·Easy·Linear Equations in One Variable
A bookstore has 150 copies of a popular novel in stock. The store sells 12 copies of the novel each day and receives no additional shipments. How many copies of the novel will remain in stock 7 days after the start of sales?
For problems about a quantity decreasing at a constant rate, first identify the starting amount, the rate of change per unit of time, and the number of time units. Multiply the rate by the time to find the total change, then add or subtract that from the starting amount as appropriate. Writing a quick expression like helps you avoid repeated subtraction and reduces mistakes under time pressure.
Hints
Think about total books sold
The store sells 12 copies every day. How can you find how many copies are sold in 7 days?
Use multiplication for repeated subtraction
Instead of subtracting 12 seven times, multiply: what is ?
Find the remaining stock
Once you know how many copies were sold in total, subtract that number from 150 to find how many are left.
Desmos Guide
Use Desmos to check the calculation
In Desmos, type the expression 150 - 12*7 and press Enter. The value that appears is the number of copies remaining after 7 days; choose the answer option that matches this value.
Step-by-step Explanation
Identify the starting amount and the daily change
The bookstore begins with 150 copies.
Each day, it sells 12 copies and receives no new copies, so the number of books in stock goes down by 12 each day.
We want to know how many are left after 7 days of selling.
Find how many copies are sold in 7 days
Since the store sells 12 copies each day, in 7 days the total number of copies sold is
Calculate to get the total number of books sold over the 7 days.
Subtract the total sold from the starting amount
From Step 2, , so 84 copies are sold in 7 days.
Now subtract this from the starting 150 copies:
So, 66 copies of the novel will remain in stock after 7 days. This matches choice A) 66.