CalcElfCalcElf › Shared work: 15 days and 30 days alone
Shared work: 15 days and 30 days alone
One worker alone can finish a job in 15 days, and another alone can finish the same job in 30 days. Working together, how many days do they need?
Answer
10 days
Step-by-step
- 1 ÷ 15 = 0.0667Work done per day by A
- 1 ÷ 30 = 0.0333Work done per day by B
- 1 ÷ (0.0667 + 0.0333) = 10Combined time = 1 ÷ combined rate
Why it works
Working together, the two work rates add: each rate is 1 divided by that person's own time, so the shared time is 1 divided by the sum of the two rates.
Common mistakes
- Taking the average of 15 and 30 days.
- Adding the two times and using that sum as the answer.