book Maths Puzzle Numerical Ability

Curly can do a job in 30 min, Larry can do it in 40 min, and Moe can do it in 60 min. How long will it take them if they work together?

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book Other Question

The half-life of Bismuth is 5 days. Then 75% of an original amount will cease to be radioactive in 10 days. I believe that this one is true. Am I right? Can you please help me? I am really confused.

Bobby and Rick are in a 10-lap race on a one-mile oval track. Bobby, averaging 90 mph has completed two laps just as Rick is gettin