Only part of the work done in the first days: how many more men to finish on time

The same question, asked 3 times: CDS 1 2018*, CDS 2 2021*, CDS 2 2022. Every wording below, oldest first.

Try each one first, then open its answer.

Question 1
CDS 1 2018
26 $A man undertakes to do a certain work in 150 days. He employs 200 men. He finds that only a quarter of the work is done in 50 days. How many additional men should he employ so that the whole work is finished in time?$
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Question 2
CDS 2 2021
6 $20 men are supposed to complete a work in 10 days. After working for 5 days, they realise that only one-fourth of the work is done. How many more men they need to employ to finish the work on time ?$
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Question 3
CDS 2 2022
14 $480 persons working 10 hours per day complete one-fourth of a work in 10 days. How many additional persons are to be employed in order to complete the remaining work in 20 days, working 8 hours per day ?$
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Question 1