**Sol: **Ratio of efficiency = 2:1 (A:B)

Ratio of required time = 1:2 (A:B) x:2x

but 2x-x=30

x= 30 and 2x= 60

Now efficiency of A =3.33% and efficiency of B =1.66%

Combined efficiency of A and B together = 5%

time required by A and B working together to finish the work = = 20 days

Note: Efficiency

Efficiency time = Constant Work

Hence, Required time =

whole work is always cosidered as 1, in terms of fraction and 100%, in terms of percentage.

In, general no.of days or hours =

A) 8 hrs | B) 12 hrs |

C) 6 hrs | D) 4 hrs |

Explanation:

Suppose A, B and C take x, x/2 and x/3 respectively to finish the work.

A) 87.5 | B) 89 |

C) 91.5 | D) 93.5 |

Explanation:

We have M1 D1 H1 / W1 = M2 D2 H2 / W2 (Variation rule)

(60 x 30 x 8)/ 150 = (35 x D2 x 6) / 200

D2 = (60 x 30 x 8 x 200) / (150 x 35 x 6) => D2 = 91.42 days =~ 91.5 days.

A) 8.7 hrs | B) 5.2 hrs |

C) 5 hrs | D) 7.5 hrs |

Explanation:

Ratio of times taken by A and B = 160 : 100

A can do the work in 12 days

Let B can do the work in "D" days

=> 160:100 = 12 : D

=> D = 12 x 100/160 = 7.5 hrs

A) Total work | B) One-fourth work |

C) Half work | D) Two-third work |

Explanation:

A can do the work = 18 days

B can do the work = 18/2 = 9 days

(A + B)'s 1 day work = 1/18 + 1/9 = 1/6

=> In 3 days = 3x1/6 = 1/2 work is completed.

A) 13 days | B) 10 days |

C) 7 days | D) 16 days |

Explanation:

1 boy's 1 day work = 1/70

1 girl's 1 day work = 1/140

(5 boys + 10 girls)'s 1 day work

= (5/70 + 10/140) = (1/14 + 1/14) = 1/7

5 boys and 10 girls will complete the work in 7 days.