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Unitary Method Problem

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by GMATGuruNY » Sat Oct 10, 2015 1:18 am
[email protected] wrote:15 labourers can fill 35 boxes in 7 days. How many labourers can fill 65 boxes in 5 days ?

(a) 13

(b) 39

(c) 45

(d) 65
Use the following formula:

(workers * time)/(output) = (workers * time)/(output)

Since 15 workers require 7 days to fill 35 boxes, and we must determine how many workers in 5 days can fill 65 boxes, we get:

(15 * 7)/35 = (x * 5)/65
3 = x/13
x = 39.

The correct answer is B.
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by theCEO » Sat Oct 10, 2015 1:19 am
[email protected] wrote:15 labourers can fill 35 boxes in 7 days. How many labourers can fill 65 boxes in 5 days ?

(a) 13

(b) 39

(c) 45

(d) 65
There are 3 items. The key is to change the 2 items at once and leave the other constant.

07days ..... 15men ..... 35boxes
01days ..... 15men ..... 05boxes
here we changed the ratio of days and boxes and kept men constant

01days ..... 15men ..... 05boxes
13days ..... 15men ..... 65boxes
here we changed the ratio of days and boxes and kept men constant

13days ..... 15men ..... 65boxes
13days x (5/13) ..... 15men x (13/5) ..... 65boxes
if we decrease the number of days by x, we have to decrease the number of men by 1/x

13days x (5/13) ..... 15men x (13/5) ..... 65boxes
5days ..... 39men ..... 65boxes

ans = b
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