Answer:
a) 2 new printers
b) 11 min
Explanation:
Given:
5 old printers take 30 min to produce a batch of comic books
4 new printers take 18 min to produce a batch of comic books
.
a) First, we need to find how long does one old and new printer take to produce a batch of comic books:
.
Since 5 old printers take 30 min to do the job, one printer would take 5 times more than this (5 printers work together and they do the job faster than one, that's why we have to multiply):
.
1 old printer does the job in:
5 × 30 = 150 min
1 new printer does the job in:
4 × 18 = 72 min
.
Since one old printer does the job in 150 min, 6 old printers would do this job 6 times faster (that's why we divide):
6 old printers would take:
150 / 6 = 25 min
2 new printers would take:
72 / 2 = 36 min
.
25 < 36
That means, 2 new printers would do this job faster
.
b) In order to find how much less time would this take, we have to subtract:
.
36 - 25 = 11 min