P and Q together can complete a work in 20 days. If Q alone can complete the work in 25 days, then in how many days P alone can complete the same work ?

25 days 100 days 20 days 50 days

100 days

Time taken by P alone to complete the work = $\frac{total\; work}{efficiency}$   = $\frac{100}{1}$                                      = 100 days