Multiple choice

A team of 15 technicians was assigned to complete a network installation project in 45 days. However, after a certain number of days, they increased their working efficiency by 20% and finished the project five days ahead of schedule. How many days after starting the project did they increase their efficiency?

  1. 10 days

  2. 12 days

  3. 15 days

  4. 18 days

  5. 21 days
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The total work is 15 technicians * 45 days = 675 man-days. Let x be the days worked at normal efficiency. The remaining (45 - x) days were finished in (45 - 5 - x) = (40 - x) days at 1.2 efficiency. Thus, 15x + 15 * 1.2 * (40 - x) = 675. Solving for x gives 15x + 18(40 - x) = 675, so 15x + 720 - 18x = 675, which leads to 3x = 45, or x = 15.

AI explanation

The total work is 15 technicians multiplied by 45 days, which equals 675 man-days. The team finished 5 days ahead of schedule, meaning they worked for 40 days. Letting x be the number of days they worked at normal efficiency, the equation is 15x plus 18(40 minus x) equaling 675, where 18 reflects the 20 percent increase in daily efficiency. Solving 15x plus 720 minus 18x equals 675 gives 3x equals 45, so x is 15 days.

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