Multiple choice

A can do a job in $10$ days and B in $20$ days. They work together but $4$ days before the finish of the job B leaves. Find the total days to finish the job?

  1. $6$
  2. $8$
  3. $12$
  4. $14$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let x be the total days. A works for x days, B works for x-4 days. (x/10) + ((x-4)/20) = 1. Multiplying by 20 gives 2x + x - 4 = 20, so 3x = 24, x = 8.

AI explanation

Using the formula for work rates, 1/A equals 1/10 and 1/B equals 1/20. Let the total time be T days; then A works for T days and B works for (T minus 4) days. The equation is T divided by 10 plus (T minus 4) divided by 20 equals 1. Multiplying by 20 gives 2T plus T minus 4 equals 20, so 3T equals 24 and T equals 8 days.

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