This can be treated as a ratio problem. From 3:15 to 3:20 is 5 minutes. Scott printed 12 pages in 5 minutes. That is 12 to 5. You want to know how long it will take Scott to print 15 pages at this rate. Equal the 12 to 5 ratio to 15 to “unknown time” or “t” .

12/5=15/t

Multiply both sides by 5 and t.

t*(12/5)=(15/t)*t

5*(12t/5)=15*5

12t=75

t=75/12

t=6.25 or 6 minutes and 25 seconds

 

 

If you need to know how much longer it will take to finish printing than. you look at it like this; it took 5min to complete 12 pages and he has 3 pages left to print. Therefore 5/12=x/3, then cross multiple to get 12x=15, then get x by itself so divide both sides by 12, x=15/12, so x=1.25min or 1min 15 sec.

Any type of ratio problem like this, just cross multiply: You have (12/5) = (15/x).  You get 12(x) = 75

x = 6.25 min or 6 min and 15 seconds.

In five minutes, he printed 12 pages.  At this rate, in how many minutes did he print 15 pages?

Quick approach: 5:12 = t:15

Solve for t,

t = 25/4 = 6.25 minutes