**Rule 7:**

If A can do a piece of work in D_{1} days, B can do in D_{2} days and C can do in D_{3} days then they together can do the same work in

**If A can do a piece of work in 30 days, B can do in 24 days and C can do in 20 days then they together can do the same work in _____ days.**

**Sol:**

**Rule 8:**

If A and B together can do a piece of work in D_{1} days and A alone can do it in D_{2} days, then B alone can do the work in

**Jack and Jill together can do a piece of work in 10 days. Jack alone can do it in 15 days. In how many days can Jill alone do it?**

**Sol:**

Let’s say D_{1} = 10, D_{2} = 15

**Rule 9:**

If the number of men are changed in the ratio of m:n, then the time taken to complete the work will change in the ratio n:m