Brain Teasers & Mental Math
Pipe A fills a tank in 3 hours; pipe B fills it in 6 hours. Running together, how long to fill the tank?
Model answer
2 hours.
Add the RATES, not the times: A fills 1/3 of the tank per hour, B fills 1/6. Together: 1/3 + 1/6 = 1/2 tank per hour → 2 hours.
Shortcut formula for two workers: time…
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