Multiple choice

From a full barrel containing 729 litres of honey we pour off 'a' litre and add water to fill up the barrel. After stirring the solution thoroughly, we pour off 'a' litre of the solution and again add water to fill up the barrel. After the procedure is repeated 6 times, the solution in the barrel contains 64 litres of honey. Find a.

  1. 243 litres

  2. 81 litres

  3. 2.7 litres

  4. 3 litres
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The formula for remaining honey is Initial * (1 - a/V)^n = Final. 729 * (1 - a/729)^6 = 64. (1 - a/729)^6 = 64/729 = (2/3)^6. So 1 - a/729 = 2/3, which means a/729 = 1/3, so a = 243.

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