Multiple choice

Anjali alone can do a piece of work in (x) days and Shalu alone can do the same work in (x+5) days. If Anjali and Shalu together can complete the same work in (11\frac{1}{9}) days, then find the number of days required by Anjali to complete the work alone?

  1. 25 days

  2. 15 days

  3. 10 days

  4. 20 days

  5. None of these

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work rate formula: If Anjali takes x days and Shalu takes (x+5) days alone, their combined rate is 1/x + 1/(x+5) = 1/(11⅑) = 9/100. Solving: (2x+5)/(x²+5x) = 9/100, which gives 9x² + 45x - 200x - 500 = 0, or 9x² - 155x - 500 = 0. Using quadratic formula: x = [155 ± √(24025 + 18000)]/18 = [155 ± √42025]/18 = [155 ± 205]/18. Since x must be positive, x = (155 + 205)/18 = 360/18 = 20. Therefore Anjali alone takes 20 days.