Question

a library loans out 3 books every day for a week and no books are returned. the equation below is written to represent the situation:
$(-3)\cdot7=-21$
which description best explains the meaning of $-21$ in the equation?
a books were loaned out for $-21$ days.
b the library now has $-21$ books.
c the change in the number of books at the library over the course of the week was $-21$.
d the number of books loaned per day was $-21$.

Explanation:

• Option A: Days cannot be negative in this context.
• Option B: The library can't have a negative number of books in a practical sense.
• Option C: Since 3 books are loaned out each day (negative change as books are leaving) for 7 days, the total change in the number of books is \((- 3)\times7=-21\). This makes sense as it represents the overall decrease (change) in the number of books over the week.
• Option D: The number of books loaned per day is 3, not -21.

Answer:

C. The change in the number of books at the library over the course of the week was \(-21\).