More men join partway through: days for the remaining work

This type of question, asked 2 times: 18 Jul 2023 S1, 20 Sep 2025 S1. All 3 questions below, oldest first.

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Question 1
18 Jul 2023 S1
64 $10 men can do a work in 25 days. After 12 days of work, 3 more men were engaged to finish the work. The number of days required to complete the remaining work is:$
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Question 2
18 Jul 2023 S1
52 $30 men can complete a work in 12 days. After 6 days, 24 more men joined them. How many days will they now take to complete the remaining work?$
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Question 3
20 Sep 2025 S1
54 $A contractor employs 15 men to complete a work in 24 days, working 8 hours per day. After six days, he adds five more men but also reduces the working hours to six per day from the seventh day onwards. If all men work with the same efficiency throughout, how many more days will be required to finish the remaining work?$
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Question 1