P can do a piece of work in 20 days and Q can do it in 25 days. If they work on it together for 4 days, then what percentage of work will be left?

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SSC GD Constable (2022) Official Paper (Held On : 08 Feb 2023 Shift 1)
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  1. 68%
  2. 52%
  3. 64%
  4. 36%

Answer (Detailed Solution Below)

Option 3 : 64%
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Data:

P's work rate (Wp) = 1/20 work/day

Q's work rate (Wq) = 1/25 work/day

Time worked together (t) = 4 days

Concept:

The combined work rate of P and Q is Wp + Wq.

The amount of work done is the product of the work rate and time.

Solution:

Step 1: Find combined work rate:

⇒ W = Wp + Wq = 1/20 + 1/25 = 9/100 work/day

Step 2: Find work done together in 4 days:

⇒ Work_done = W × t = 9/100 × 4 = 36/100 = 0.36 of the work

Step 3: Calculate percentage of work left:

⇒ Work_left = 1 - Work_done = 1 - 0.36 = 0.64 = 64%

Hence, 64% of the work will be left.

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