towerSpider wrote:Any short method (just like stacey's for mixtures) for work problems. I mean one short formula that can work for all. They are hardest of all questions.
Questions of such type are like if three men can do a certain job in twelve hours, if two men are employed then how long will it take to do two third of job?
Approach #1:
When the job is undefined, we can plug in our own values.
Plug in rate for each man = 1/hour.
Rate for 3 men = 3/hour.
Work for 12 hours = r*t = 3*12 = 36. This is the value of the job.
2/3 of the job = (2/3)*36 = 24.
Rate for 2 men = 2/hour.
Time = w/r = 24/2 = 12 hours.
Approach #2:
(number of men) x (number of days) always has to yield the same amount of work.
So we could set up this equation:
(number of men) x (number of days) = (number of men) x (number of days)
3 * 12 = 2x
x = 18
Since 2 men would need 18 days to complete the whole job, (2/3)*18 = 12 days will be needed to complete 2/3 of the job.
In math terms, the number of men is
inversely proportional to the number of days. When two values are inversely proportional, as one value goes down, the other must go up, so that their product is always the same. In the problem above, as the number of men goes down, the number of days must go up, so that the product of the 2 values stays the same and we're always getting the same amount of work done.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at
[email protected].
Student Review #1
Student Review #2
Student Review #3
