Time & work

Time & Work:

                     Important formula on  Time & Work.

1. Work from Days:

   If A can do a piece of work in n days, then A's 1 day's work =	1	.
   	n

2. Days from Work:

   If A's 1 day's work =	1	,	then A can finish the work in n days.
   	n

3. Ratio:
   If A is thrice as good a workman as B, then:
   Ratio of work done by A and B = 3 : 1.
   Ratio of times taken by A and B to finish a work = 1 : 3

A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :

A)   1/4        B)   1/10           C)   7/15            D)8/15 A's 1 day's work = 1 ; 15 B's 1 day's work = 1 ; 20 (A + B)'s 1 day's work = 1 + 1 = 7 . 15 20 60                                                                            ~ First find out 1 day work (A + B)'s 4 day's work = 7 x 4 = 7 . 60 15                                                                            ~ After multiplication with 4 days Therefore, Remaining work = 1 - 7 = 8 . 15 15 A can lay railway track between two given stations in 16 days and B can do the same job in 12 days. With help of C, they did the job in 4 days only. Then, C alone can do the job in: A. 9 1 days 5 B. 9 2 days 5 C. 9 3 days 5 D. 10

(A + B + C)'s 1 day's work =	1	,
	4

A's 1 day's work =	1	,
	16

B's 1 day's work =	1	.
	12

C's 1 day's work =	1	-		1	+	1		=		1	-	7		=	5	.
	4			16		12				4		48			48

So, C alone can do the work in

48/5   =

1