Multiple choice

If $ A$ and$ B$ together can complete a piece of work in $15$ days and $ B$ alone in $ 20$ days. In how many days a alone can complete the work ?

  1. $30$ days
  2. $60$ days
  3. $15$ days
  4. $45$ days
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let A's work rate be 1/a and B's be 1/b. Given 1/a + 1/b = 1/15 and 1/b = 1/20. Then 1/a = 1/15 - 1/20 = 4/60 - 3/60 = 1/60. So A takes 60 days.

AI explanation

The total work can be found using the LCM of 15 and 20, which is 60 units. A and B together complete 4 units per day (60/15), while B alone completes 3 units per day (60/20). A's daily work is the difference, which is 4 - 3 = 1 unit per day. At 1 unit per day, A alone will take 60 days to finish the 60 units of work.

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