Matthew can build a block wall in 3 days. Andy can build the wall in 5 days. How long will it take if they work together?

Question

I just need to see how to do this type of problem since it's been a while since I last did one like this

Answer 1

Matt can do 1/3 of the job in 1 day and Andy can do 1/5 of the job in 1 day. Together, they can do 1/x of the job in 1 day. The variable x represents the number of days it will take them to complete the job if working together. 

 

1/3 + 1/5 = 1/x

 

5x + 3x = 15

 

8x = 15

 

x = 15/8 = 1 7/8 days