Question

Hey Guys!
can you help me with this?

Father can paint the house alone in 8 hours and it takes his son 12 hours to do the same job. How many hours does it take if they work together to complete the job?

Answer 1

IDK how to do this, sorry.

Answer 2

its ok @mipie13

Answer 3

4.8 hours

Answer 4

There is a formula for this:
f = 8
s = 12

time = 8*12 / 8+12 = 96 / 20
= 4.8 hours

Answer 5

Father can do 1/8 of the job in 1 hours. His son can do 1/12 of the job in 1 hours. So in two hours, they can do 1/8+1/12 of the job = 5/24 of the job.They can do 5/24 of the job in 1 hour, times each side by 4.8 , you get 4.8 hours

Answer 6

father in one hour do 1/8 of work and son do 1/12 of work.if both work in x hours :we have ;1/12(x)+1/8(x)=1
2/24(x)+3/24(x)=1
x=24/5=4.8 hours

Answer 7

@fazeli where did the 24 came from?

Answer 8

is it the LCM?

Answer 9

\[\frac{ 1 }{ 12}x+\frac{ 1 }{ 8 }x=1\]
\[\frac{ 2 }{ 24 }x+\frac{ 3 }{ 24}x=1\]

Answer 10

4.8

Answer 11

thanks @fazeli
and @josjos

also at @wolf1728