Answer :
Given:
Original number of books = 15 books
New number of books = 21 books
Let's find the percentage change.
To find the percentage change, apply the formula below:
[tex]\text{Percentage change = }\frac{New\text{ value - Original value}}{Original\text{ value}}\ast\frac{100}{1}[/tex]Input values into the formula.
We have:
[tex]\begin{gathered} \text{Percentage change = }\frac{21-15}{15}\ast\frac{100}{1} \\ \\ \text{Percentage change = }\frac{6}{15}\ast\frac{100}{1} \\ \\ \text{Percentage change = }0.4\ast100=40\text{ \%} \end{gathered}[/tex]Therefore, the percentage change is 40 percent.
ANSWER:
40%