Multiple choice

A works twice as fast as B. If B can complete a work in $12$ days independently, then the number of days in which A and B can together finish the work is:

  1. $4$ days
  2. $6$ days
  3. $8$ days
  4. $18$ days
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

B takes 12 days, so B's rate is 1/12. A is twice as fast, so A's rate is 2/12 = 1/6. Combined rate = 1/12 + 1/6 = 3/12 = 1/4. Together they take 4 days.

AI explanation

Since A works twice as fast as B, A can complete the work in 6 days while B takes 12 days. Taking the Least Common Multiple of 6 and 12 as 12 units of total work, A does 2 units per day and B does 1 unit per day. Working together they complete 3 units daily, so they finish the 12 units in 4 days.

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