If 6 men can do a piece of work in 30 days of 9 hours each, how many men will it take to do 10 times the amount of work if they work for 25 days of 8 hours?
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I used the formula M1 D1 H1 / W1 = M2 D2 H2 / W2. Plugged in 6 men, 30 days, 9 hours for 1 work, then solved for M2 with 25 days, 8 hours, and 10 work. Got 81. Is that right? Seems too clean but it's a 505-555 question so maybe.
Yes, that's exactly how I did it. 81 is one of the choices, so you're good.
I made the mistake of using 10 as the work for the first scenario instead of the second. Classic. Once I fixed that, it was straightforward.
Why is D correct? I got 81 but I want to be sure there's no trick with the '10 times the amount of work' wording. Does 'amount of work' refer to the total work or the rate?
It's total work. The original work is 1 unit, so 10 times is 10 units. The formula handles it as long as you keep the work proportional.
Quick way: men needed is proportional to work and inversely proportional to days and hours. So required men = 6 * 10 * (30*9)/(25*8) = 81. Nice and fast.
This one was pretty easy once you set up the proportion. I did it in under a minute. Good confidence booster.
What it tests
Your ability to combine individual work rates, usually by working with the fraction of a job completed per unit of time.
Common trap
Adding the times instead of the rates, or forgetting to take the reciprocal when combining rates.