rates and formulae.

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ildude02: Master | Next Rank: 500 Posts; Posts: 320; Joined: Sun Jan 13, 2008 10:00 pm; Thanked: 10 times

rates and formulae.

by ildude02 » Sun Jul 13, 2008 7:37 am

A's rate is twice that of B and 1/3 that of C. They all combined to produce 2700 units, how many units did C produce?

a)300
b)600
c)900
d)1200
e)1800

My question is, I always get confused when to sum them all up and equate to the total and when we should use the formulae; 1/A +1/B +1/C = 1/T; where T is the total time, and then you derive the units based off the individual time. Can someone clarify this for me? Thanks!

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Source: Beat The GMAT — Problem Solving | Sun Jul 13, 2008 7:37 am

raunekk: Legendary Member; Posts: 1159; Joined: Wed Apr 16, 2008 10:35 pm; Thanked: 56 times

by raunekk » Sun Jul 13, 2008 8:44 am

IMO:E (1800)

IF you are given total time taken to do a job by a person or a machine,

then you need to use the formula 1/a+1/b.This will give you work done per-hour by each machine individually.That is, rate.

But if u are directly given time or rate/hour of each component you dont need to use that formula..you can directly use w=rt.

This is what you are asking rite??

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ildude02: Master | Next Rank: 500 Posts; Posts: 320; Joined: Sun Jan 13, 2008 10:00 pm; Thanked: 10 times

by ildude02 » Sun Jul 13, 2008 8:48 am

So you just add them up to get 9x and find x instead of using the formula?

Also, isn't there a formuale for even units along with time?

Units of A/TimeA + Unites B/TimeB = Total Units/TotalTime; when do we use this formulae? If we are given indivdual times and units produced by each of them and asked to find the missing units?

Appreciate your response.

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sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pm; Location: INDIA; Thanked: 84 times; Followed by:3 members