if it takes john 30min to do a job, and 1hr for peter to do the same job. how long will it take the two if they work together.
i know its probably too easy.... can i also have the underlining formular if there is any. i came up with 45 but i doubt it lol.
also plz show me how to work it out so i can tell my wife i did it lol. thanks in advance to those who will participate...
2007-04-19 20:37:06 · 26 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
20 minutes is actually correct.
In each minute John does 1/30 of the job and Peter does 1/60, so together they do 1/30 + 1/60 = 2/60 + 1/60 = 3/60 = 1/20 of the job. So it takes 20 minutes to do the whole job.
In general if one person can do it in x minutes and another can do it in y minutes, together they should be able to do it in
xy / (x+y) minutes. In this case we have 30×60 / 90 = 20 minutes.
2007-04-19 20:50:12 · answer #1 · answered by Scarlet Manuka 7 · 4⤊ 1⤋
John will do some work in 1 minute of: 1/30
Peter will do the same amount of work in 1/60 minutes
Both working together will do 1/30 + 1/60 = 3/60 = 1/20
So in unit time the work will be the reciprocal of: 1/20 = 20 minutes
Hope this helps and if you like it vote for it!!
2007-04-20 08:28:40 · answer #2 · answered by Anonymous · 0⤊ 0⤋
Please explain why your wife is going to leave you over a math problem? That sounds interesting. Oh, and Trish is right with 20 minutes. John will do 2/3 of the job (20/30) and Peter will do 1/3 of the job (20/60). 1/3 + 2/3 = 1.
2007-04-19 20:43:29 · answer #3 · answered by bhalpern123 2 · 3⤊ 0⤋
There are many different people who have come up with the correct answer with many different ways of solving it. When attempting this kind of question, try to get an idea in your head as to what the answer will roughly be. So if John can do the job in 30 minutes the two people combined must be able to do it in less than 30 minutes.
2007-04-20 13:44:20 · answer #4 · answered by brainyandy 6 · 0⤊ 0⤋
20 minutes is the right answer!
John takes 30 mins, peter takes an hour. That is Peter takes double the time than John.
If you give 10 mins of John's work to Peter, he will finish that in 20 mins. Paralelly John is working his 20 mins.
2007-04-19 20:52:37 · answer #5 · answered by Phil 3 · 1⤊ 0⤋
Some people say it is 45 minutes, but they are wrong.
Think about this. One person takes 30 minutes to do one job. Now he has help.
If they both worked at the same speed, then each could do half the of 30 minutes.
One guy works twice as fast as the other guy.
Fast guy = x, slow guy = .5x
x + .5x = 30
1.5x = 30
x = 20 minutes
2007-04-19 21:56:37 · answer #6 · answered by Tasm 6 · 1⤊ 0⤋
Think of it this way. let's say the job is mailing 60 letters. If John can do it in 30 minutes, his rate is 2 letters/min. Peter's rate is 1 letter/min. If they work together to mail 60 letters, at the 20 minute mark, John would have mailed 40 letters because his rate is 2 letters/minute. Peter would have mailed 20 letters because his rate is 1 letter/min. 40 + 20 = 60 letters (at which time they finish the job).
So it takes 20 minutes.
2007-04-19 20:52:32 · answer #7 · answered by mandrake 2 · 2⤊ 1⤋
In a single hour, John can do 2 jobs and Peter can do 1 job. So, in jobs/hr, together they combine to do 3.
3 jobs/hr means that they do 1 job every 20 minutes.
For those who said 45 minutes: Don't you think it was a little funny that John by himself was doing it _faster_ than John and Peter working together?
2007-04-19 20:51:58 · answer #8 · answered by Jonny Jo 3 · 3⤊ 1⤋
4 days.
Why so long? Well, John brings Peter a beer. They sit and discuss said job. Then an hour later, they are out of beer. So, they hop in a cab (nope no drinking and driving here) to get more beer. Enroute to store, they need money. So, they stop at the banks and take out some money. Oh, who's that? That's Dave. He's going to the strippers. Well, now, John, Peter and Dave are off to the strippers. So the boys sit down watch strippers, have more beers, do more discussion of job and nagging wife, and then finally decide to venture home drunk as you please. Once home, wife is waiting for John to do his job. Realizing he spend a bunch of cash on booze and is drunk beyond belief, she punches him in the nose. Knocks him out and he doesn't regain full use of his head for 3 days. On the 4th, under the threat no sex until job is done, he gets job done.
Now, that WAS indeed easy.
2007-04-19 20:50:05 · answer #9 · answered by nightowl_2134 2 · 4⤊ 1⤋
As a reality check, if one of them can do it in 30 minutes, both of them working together can do it in less than 30 minutes.
Express both workers' times in hours.
x = time for both working together
x / (1/2) + x / 1 = 1
2x + x = 1
3x = 1
x = 1/3 hour = 20 minutes
It will take them 20 minutes working together.
2007-04-19 22:21:49 · answer #10 · answered by Northstar 7 · 0⤊ 0⤋