Multiple choice

Tinu takes 9 days more than his father to do a certain piece of work. Together they can do the work in 6 days. How many days will Tinu take to do that work alone.

  1. 12

  2. 18

  3. 15

  4. 16
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let Tinu's time be x days and father's time be x-9 days. Their combined rate is 1/x + 1/(x-9) = 1/6. Solving this quadratic equation x^2 - 21x + 54 = 0 gives x=18 or x=3. Since x must be greater than 9, Tinu takes 18 days.

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