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Trij can paint a wall alone in 7.2 days while Madhu takes 10.8 days for the same work. Working together, how many days will they take to paint 5/6 of the wall?
A4.8
B3.9
C3.6
D4.2
Answer & Solution
Correct answer: C. 3.6
1. Combined rate = 1/7.2 + 1/10.8 walls per day = 5/36 + 1/10.8; LCM gives rate = 5/21.6 per day.
2. One full wall together takes 1 ÷ (5/21.6) = 4.32 days.
3. For 5/6 of the wall: 4.32 × 5/6 = 3.6 days.
_Source: RRB Group D CEN-02/2018 PYQ, Q.30._
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