A can do 20% of a job in 7 days and B can do 25% of the job in 7 days if they worked alone. How much of the job (in percentage) can they complete in 7 days if they worked together?

Correct option is D

A can do 20% of a job = 7 days
100% job do = 7 × 5 = 35 days
B can do 25% of the job = 7 days
100% of the job do = 7 × 4 = 28 days
ATQ,
A × 35 = B × 28
A/B = 4/5
Total work = A × 35 = 4 × 35 = 140 units
Both work together for 7 days = (5 + 4) × 7
= 9 × 7 = 63 units
Percentage job complete in 7 days = (63 × 100) / 140
= 45%