21 binders can bind 1400 books in 15 days. How many binders will be required to bind 800 books in 20 days:

by

A. 6
B. 9
C. 10
D. 13

🧠 Explanation (Math):

Given: 21 binders bind 1400 books in 15 days; find binders for 800 books in 20 days
Step 1: Binders ∝ (books)/(days)
Step 2: n = 21 × (800/1400) × (15/20) = 21 × (4/7) × (3/4) = 9
Final Answer: 9