Multiple choice

A and B can do a piece of work in 6 days. B and C can do it in 7½ days. C and A can do it in 10 days. In how many days will B alone finish it?

  1. 30 days

  2. 10 days

  3. 15 days

  4. 1/10 days
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

( A + B ) 's  1 day work  = 1 / 6( B + C ) 's 1 day work = 2 / 15       ( 7 1/2 = 15 /2 ) ( C + A )'s 1 day work = 1/ 10By adding

( A+ B ) + ( B + C ) + ( C + A ) 's 1 day work = 1/ 6 + 2/15 + 1/10  (A + B + B + C + C + A) 's 1 day work = 1/ 6 + 2/15 + 1/10  ( 2A + 2B + 2C ) 's 1 day work = 1/6 + 2/15 + 1/10 2 ( A + B + C ) 's 1 day work = (5 + 4 + 3) /30 = 12/30 = 6 /15 (A + B + C )'s 1 day work = 6/15 x 2 = 6/30

( A + B + C ) 's 1 day work - ( C + A ) 's 1 day work =                                  6/30 - 1/10                                 = 6 - 3 /30                                = 3/30                                  = 1 /10 B1 day work is 1/10 B can complete whole work in  1 / 1/10 = 10 days

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