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Prep question

by isisalaska » Thu May 03, 2007 10:00 am
Working together at their contant rates, machine A makes 100 copies in 12 minutes and machine B 150 copies in 10 minutes. How many copies would they make in 30 minutes working together?
a) 250
b) 425
c) 675
d) 700
e) 750
Last edited by isisalaska on Fri May 04, 2007 6:19 am, edited 1 time in total.
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Re: Prep question

by jayhawk2001 » Thu May 03, 2007 8:49 pm
isisalaska wrote:Working together at their contant rates, machine A makes 100 copies in 12 minutes and machine B 150 copies in 10 minutes. How many copies would they make in 20 minutes working together?
a) 250
b) 425
c) 675
d) 700
e) 750
Hmm, I'm not sure I understand the question correctly. Is the first
phrase of the sentence "working together at their constant rates" ?

A makes 100/12 copies in 1 minute
B makes 150/10 copies in 1 minute

A and B together can make 100/12 + 150/10 copies in 1 min

So, in 20 minutes, they can make 20 * (100/12 + 150/10) = 466.67
copies.

This is obviously not one of the answers. I'm stumped.
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by isisalaska » Fri May 04, 2007 6:21 am
My fault, it should read 30 minutes instead of 20. I changed it.

So the answer is 700
100/12 + 150/10= 8.5+15= 23.33 x 30min. = 700 copies
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by Neo2000 » Fri May 04, 2007 8:26 am
If you have observed the numbers carefully

MAchine A will make 50copies in 6minutes or 50x5 copies in 6x5 mins=
250copies in 30mins

Similary Machine B will make 150x3 copies in 10x3 minutes

So total number of copies = 250 +450 = 700
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by Cybermusings » Fri May 04, 2007 11:34 am
Working together at their contant rates, machine A makes 100 copies in 12 minutes and machine B 150 copies in 10 minutes. How many copies would they make in 30 minutes working together?
a) 250
b) 425
c) 675
d) 700
e) 750

A --- 100 copies in 12 min
or 100/12 copies in 1 min

B ---- 150 copies in 10 min
or 15 copies in 1 min

30 min --- A 100*30/12 copies and B will make 15*30 copies
= 250 + 450 copies
= 700 copies
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