# Trouble figuring out what method to use, HELP!

• May 9th 2008, 07:59 PM
mak15
Trouble figuring out what method to use, HELP!
Dear all, I don't think this is difficult, but I am stuck........

If Steven can mix 20 drinks in 5 minutes, Sue can mix 20 drinks in 10 minutes, and Jack can mix 20 drinks in 15 minutes, how much time will it take all 3 of them working together to mix the 20 drinks?

What method should I use? How?

Thanks so much! (Bow)
• May 9th 2008, 08:18 PM
Jhevon
Quote:

Originally Posted by mak15
Dear all, I don't think this is difficult, but I am stuck........

If Steven can mix 20 drinks in 5 minutes, Sue can mix 20 drinks in 10 minutes, and Jack can mix 20 drinks in 15 minutes, how much time will it take all 3 of them working together to mix the 20 drinks?

What method should I use? How?

Thanks so much! (Bow)

Make Job/Time ratios and add up the rates.

Let mixing 20 drinks be a job.

Then Steven does 1/5 jobs/min,
Sue does 1/10 jobs/min, and
Jack does 1/15 jobs/min

To find how long it will take them to make 20 drinks together, add up their rates.

we have 1/5 + 1/10 + 1/15 = 11/30 = 1/(30/11)

since the time to complete 1 job is in the denominator when 1 is in the numerator, they take 30/11 mins to complete the job together, that is roughly 2.7272 minutes
• May 9th 2008, 08:20 PM
Spimon
Try finding out how many each person can make in 1 minute.
This will then lead us to being able to find out how many the whole team can make in 1 minute.

Alternatively you could find out how long it takes the whole team to make 1 drink and multiply this by 20.

Steven does 20 in 5 mins or 4 per minute.
Sue does 20 in 10 mins or 2 per minute.
Jack does 20 in 15 mins or 4/3 per minute.

All up they do 4+4+4/3 = 22/3 ~ 7.33 per minute.

20/7.33 = 2.7272

2.7272*60 = 164 seconds or 2:44mins.
• May 9th 2008, 08:31 PM
mak15
Quote:

Originally Posted by Jhevon
Make Job/Time ratios and add up the rates.

Let mixing 20 drinks be a job.

Then Steven does 1/5 jobs/min,
Sue does 1/10 jobs/min, and
Jack does 1/15 jobs/min

To find how long it will take them to make 20 drinks together, add up their rates.

we have 1/5 + 1/10 + 1/15 = 11/30 = 1/(30/11)

since the time to complete 1 job is in the denominator when 1 is in the numerator, they take 30/11 mins to complete the job together, that is roughly 2.7272 minutes

Thanks for the replies, people! Can you guys explain why the right answer was 2 minutes and 44 seconds!
• May 9th 2008, 08:34 PM
Spimon
2:44 seconds is the same as 2.72 minutes, just in Hr:Min form.

2min 44 seconds = 2(60)+44 seconds = 163 seconds.
Divide this by 60 and u get 2.72 minutes.
• May 9th 2008, 08:35 PM
Jhevon
Quote:

Originally Posted by mak15
Thanks for the replies, people! Can you guys explain why the right answer was 2 minutes and 44 seconds!

i gave you the answer. 0.727272.... minutes is 44 seconds. just multiply it by 60
• May 9th 2008, 08:42 PM
mak15
I found the answer by converted it back to 60 seconds. Thanks guys!