Algebra
posted by Katie on .
A new photocopier can make 72 copies in 2 min. When an older photocopier is working, the two photocopiers can make 72 copies in 1.5 min. How long will it take the older photocopier working alone to make 70 copies?

How would you set it up? Would it be (72/2) + (72/1.5)= (70/x)? we didn't do examples in class

new > 36 copies/min
old > n copies/min
new + old = (n+36) copies/min
(n+36)copies/min * 1.5 min = 72 copies
1.5 n + 54 = 72
1.5 n = 18
n = 12 copies/min
12 copies/min * t = 70 copies
t = 35/6 = 5.83 min 
I wrote out all those copies/ min and such for a reason. In problems like this if you keep track of the units, it is hard to go far off course.

I am stuck on this one too :(