word problem: How long would it take Rod to cut grass alone?

[kyl367]

Marcie can cut the grass in 3 hrs. working alone. When her younger brother Rod helps, it takes 2 hrs.
How long would it take Rod to cut grass alone?
grass/marcie alone = 3 hrs
grass/marcie and rod = 2 hrs

[stapel_eliz]

Marcie can cut the grass in 3 hrs. working alone. When her younger brother Rod helps, it takes 2 hrs.
How long would it take Rod to cut grass alone?

To learn how to set up and solve this sort of exercise, try here.

Once you understand the basic terms and techniques, do the standard set-up:

. . .time to complete task:
. . . . .Marcie: 3
. . . . .Rod: r
. . . . .together: 2

. . .portion completed per time unit:
. . . . .Marcie: 1/3
. . . . .Rod:
. . . . .together:

Complete the table, add the input amounts per unit time, set equal to the output amount, and solve for the variable.