17 Jun 19
@eladar saidI doped it out, knowing that I had to change hours to minutes. Is the solution correct?
@HandyAndy
Did you already know this kind of problem or logic it out?
17 Jun 19
2 edits
@HandyAndy
Yep, but changing units was not the key, combing parts of the job completed in one unit of time was the key.
I was taught..
1/5+1/3=1/t where t is total time.
8/15 =1/t so t= 15/8 or 1 and 7/8 hours.
Just used the calculator 52.5 minutes so you had some round off error I think.
17 Jun 19
@eladar saidBoth 0.333 and 0.555 are imprecise. I'll bet that's where the rounding error comes in.
@HandyAndy
Yep, but changing units was not the key, combing parts of the job completed in one unit of time was the key.
I was taught..
1/5+1/3=1/t where t is total time.
8/15 =1/t so t= 15/8 or 1 and 7/8 hours.
Just used the calculator 52.5 minutes so you had some round off error I think.
17 Jun 19
@HandyAndy
Yeah, I just put your technique into my calculator using parentheses in one long expression. It came out exactly right.
22 Jun 19
@eladar saidYou used a calculator to compute 7/8 of an hour! 😲
8/15 =1/t so t= 15/8 or 1 and 7/8 hours.
Just used the calculator 52.5 minutes so you had some round off error I think.
22 Jun 19
@wolfgang59 saidYep, if it was 6th then no problem. I am on a phone with a calculator ap.
You used a calculator to compute 7/8 of an hour! 😲
22 Jun 19
@handyandy saidThat is wrong and rather clumsy.
Approximately 1 hour and 53 minutes. Keven does 0.333 percent of the job each minute and Larry does 0.555 percent each minute. Together they complete 0.888 per cent per minute. The total job is finished after 112.6 minutes, or 1 hour and 53 minutes (minus a few seconds).
You need to find out the speed at which they work, then add the speeds to find their combined speed.
So K does a third of a job per hour.
And L does a fifth of a job per hour.
1/3 + 1/5 = 5/15 + 3/15 = 8/15
To complete one job will take them 15/8 hours or as Eladar said 1 hour and 52.5 minutes.
22 Jun 19
@wolfgang59 saidSo you did it the way I showed earlier.
That is wrong and rather clumsy.
You need to find out the speed at which they work, then add the speeds to find their combined speed.
So K does a third of a job per hour.
And L does a fifth of a job per hour.
1/3 + 1/5 = 5/15 + 3/15 = 8/15
To complete one job will take them 15/8 hours or as Eladar said 1 hour and 52.5 minutes.
22 Jun 19
@eladar saidWith an explanation for HandyAndy.
So you did it the way I showed earlier.
I guess when one is a teacher one can't stop explaining stuff.
22 Jun 19
@wolfgang59 saidHe used a rate as well. He chose to go with percent of job completed per second but made the error of rounding off intermediate calculations.
With an explanation for HandyAndy.
I guess when one is a teacher one can't stop explaining stuff.
22 Jun 19
@wolfgang59 saidThe clumsiness was replaced by the proper method. Do you have anything to add to that?
That is wrong and rather clumsy.
You need to find out the speed at which they work, then add the speeds to find their combined speed.
So K does a third of a job per hour.
And L does a fifth of a job per hour.
1/3 + 1/5 = 5/15 + 3/15 = 8/15
To complete one job will take them 15/8 hours or as Eladar said 1 hour and 52.5 minutes.
22 Jun 19
@handyandy saidI just did.
The clumsiness was replaced by the proper method. Do you have anything to add to that?