Math
posted by Anonymous on .
Can anybody help me with this? I don't understand?:
Tim paints 1 fence every two minutes. Moby paints 14 fences every two minutes. How many minutes will it take them to paint the fences, working together, if they have 150 fences to paint.

1/2 + 2/14 = x/150


2/1+14/2=150/x

Here is a common sense approach. In two minutes, they both paint 15 fences.
amount=rate*time
150fences=15fences/2min * time
time= 150*2/15=20 min
Now a more analytical approach.
The combined rate is the rate of each added.
ratecombined= 1fence/2min+14fence/2 min
= 15fence/2 min
fencestotal= ratecombined*time
150=15/2 * time and you have it. 
opps! be sure to write the units out because I accidentally wrote 2 min/1 fence instead of 1 fence/ 2 min.
1 fence/2 min +14 fence/2 min= 150 fence/x min