Multiple choice

$A$ can do a work in $15$ days and $B$ in $20$ days. If they work on it together for $4$ days, then the fraction of the work that is left is:

  1. $\cfrac{1}{4}$
  2. $\cfrac{1}{10}$
  3. $\cfrac{7}{15}$
  4. $\cfrac{8}{15}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A's rate = 1/15, B's rate = 1/20. Combined rate = 1/15 + 1/20 = 7/60. Work done in 4 days = 4 * (7/60) = 7/15. Work left = 1 - 7/15 = 8/15.

AI explanation

Using the Least Common Multiple method, let the total work be 60 units, making the daily work capacities of A and B equal to 4 units and 3 units respectively. Working together, their combined daily capacity is 7 units, so in 4 days they complete 28 units. This leaves 60 - 28 = 32 units of work remaining. The remaining fraction of the work is 32/60, which simplifies to 8/15.

Keep practicing — related questions