Work and Time Interview Questions
If 5 machines take 5 minutes to make 5 widgets, how long do 100 machines take to make 100 widgets? — spoken sample answer for Indian interviews.
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If 5 machines take 5 minutes to make 5 widgets, how long do 100 machines take to make 100 widgets?
Five machines make five widgets in five minutes, so one machine makes one widget in five minutes. A hundred machines working in parallel each make one widget in those same five minutes, so 100 widgets still take 5 minutes. People rush to 100 minutes. I would mark 5 minutes.
5 machines, 5 minutes, 5 widgets. 100 machines for 100 widgets?
One machine, one widget, 5 minutes. 100 machines, 100 widgets, still 5 minutes. Rate is 1 widget per machine per 5 minutes. Do not scale all three numbers together.
A+B in 12 days, A alone 20. B alone?
1/12 - 1/20 = 1/30, so 30 days. I check 1/20+1/30=1/12. Rates add. The check is 10 seconds.
A fills 10 min, B 15, C empties 30. Together?
1/10+1/15-1/30=2/15, time 7.5 min. Emptying is negative work. Common denominator. Infosys loves pipes.
Why do people miss the 5 machines puzzle?
They treat 5-5-5 as a proportion that should become 100-100-100. The invariant is minutes per widget per machine. Showing I know the trap is part of the answer.
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