RRB RPF RPSF SI and CONS Model Papers 8 with solutions

Question : 53 of 120

Marks: +1, -0

Three taps A, B and C can fill a tank in 12, 15 and 20 hours respectively. If A is open all the time and B and C are open for one hour each alternatively, the tank will be full in :

6 hours
$62/3$ hours
7 hours
$7 1/2$ hours

Validate

Solution:

(3) A takes 12 hrs, to fill 1 tank
∴ A takes 1 hr. to fill

1/12

tank
B takes 15 hrs. to fill 1 tank
B takes 1 hrs. to fill

1/15

tank
C takes 20 hrs. to fill 1 tank
C takes 1 hr. to fill

1/20

tank

{ {1}/{12}+ {1}/{15}}/{1 {\hr} .}+ { {1}/{20}+ {1}/{12}}/{2 {\nd} {\hr}}+ { {1}/{15}+ {1}/{12}}/{3 {\rd} {\hr}}

+{1/20+1/12}/{4\th \hr}+{1/15+1/12}/{5\th \hr }

+{1/20+1/12}/{6\th \hr}+ {1/15+1/12}/{7\th\hrs}

= {5+4+3+5+4+5+3+5+4+5+3+5+4+5}/{60}

= {60}/{60}=1=7

hrs

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