SOLUTION: If Norm and cliff together can paint a room in 4 hours, and Norm can paint the same room in 3 hours less than cliff, How long does it take cliff to paint the room by himself?

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Question 249507: If Norm and cliff together can paint a room in 4 hours, and Norm can paint the same room in 3 hours less than cliff, How long does it take cliff to paint the room by himself?
Answer by edjones(8007) About Me  (Show Source):
You can put this solution on YOUR website!
Let c=time it takes cliff to paint a room. Let n=time it takes norm.
n=c-3
Cliff can do 1/c of the job in 1 hr
Norm can do 1/(c-3) of the job in 1 hour
together they can do 1/4 the job in 1 hr.
1/(c-3) + 1/c = 1/4
4c+4(c-3)=c(c-3) multiply each side by 4c(c-3) to eliminate fractions.
4c+4c-12=c^2-3c
c^2-11c+12=0
c=9.77 hrs
.
Ed
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Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case 1x%5E2%2B-11x%2B12+=+0) has the following solutons:

x%5B12%5D+=+%28b%2B-sqrt%28+b%5E2-4ac+%29%29%2F2%5Ca

For these solutions to exist, the discriminant b%5E2-4ac should not be a negative number.

First, we need to compute the discriminant b%5E2-4ac: b%5E2-4ac=%28-11%29%5E2-4%2A1%2A12=73.

Discriminant d=73 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28--11%2B-sqrt%28+73+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%28-11%29%2Bsqrt%28+73+%29%29%2F2%5C1+=+9.77200187265877
x%5B2%5D+=+%28-%28-11%29-sqrt%28+73+%29%29%2F2%5C1+=+1.22799812734123

Quadratic expression 1x%5E2%2B-11x%2B12 can be factored:
1x%5E2%2B-11x%2B12+=+1%28x-9.77200187265877%29%2A%28x-1.22799812734123%29
Again, the answer is: 9.77200187265877, 1.22799812734123. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+1%2Ax%5E2%2B-11%2Ax%2B12+%29