I need help with a word problem in Math?

Question

Chelsea can paint the family room in 6 hours. Jake can paint the same room in 5 hours. If Chelsea starts painting it, and Jake joins her two hours later, how long will it then take them to finish painting?

Answer 1

c = 6 hours

j = 5 hours

 

Let's imagine that the room is made of 30 blocks (because 5 * 6 = 30)

6c = 30

c = 5.  So Chelsea can paint 5 blocks per hour

 

5j = 30

j = 6.  Jake can paint six blocks per hour

 

2c --> 2 * 5 = 10.  Ten blocks completed so far in the past 2 hours

 

30 - 10 = 20 blocks left

 

(c+j)h = 20

11h = 20

h = 20/11

h = 1 ⁹/₁₁ hours to complete the rest of the room.