R alone can complete a work in 40 days. S alone can complete the same work in 50 days. They work together for 10 days. What part of total work is completed?
Show answer & explanation
Correct answer: B
Explanation
R's work in 1 day = 1/40
S's work in 1 day = 1/50
Combined work in 1 day -
= 1/40 + 1/50
= (5 + 4)/200
= 9/200
Work completed in 10 days -
= 10 × 9/200
= 90/200
= 9/20