Efficiency of A + B = 33.33% = 100/3
Ratio of efficiency of A and B = 3 : 1

Correct Option: A

Efficiency of A + B = 33.33% = 100/3
Ratio of efficiency of A and B = 3 : 1
∴ Efficiency of A = (3/4) x 33.33 = 25%
∴ Number of days taken by A = 100/25 = 4

Efficiency of A + B = 100/(20/3) = 15%
No. of days ( A:B ) = 4 : 5
Efficiency ( A:B ) = 5 : 4

Correct Option: A

Efficiency of A + B = 100/(20/3) = 15%
No. of days ( A:B ) = 4 : 5
Efficiency ( A:B ) = 5 : 4

∴ Efficiency of B = (4/9) x 15 = 20/3 = 6²/₃%

A : B : C
Ratio of efficiency 3 : 1 : 2
Ratio of number of days { 1/3 : 1/1 : 1/2 }

Correct Option: A

A : B : C
Ratio of efficiency 3 : 1 : 2
Ratio of number of days { 1/3 : 1/1 : 1/2 }
or 2 : 6 : 3
Hence, (a) is correct [ Time = 1/ Efficiency ]

Efficiency of A = 100/24 = 4.16%
Efficiency of B = 100/30 = 3.33%
Efficiency of (A+ B+C) =100/12 = 8.33%

∴ Efficiency of C = (8.33) - (4.16 + 3.33) = 0.83%

Correct Option: B

Efficiency of A = 100/24 = 4.16%
Efficiency of B = 100/30 = 3.33%
Efficiency of (A+ B+C) =100/12 = 8.33%

∴ Efficiency of C = (8.33) - (4.16 + 3.33) = 0.83%
∴ Number of days required by C to complete the work alone
= 100/0.83 = 100/(5/6) = 120 days
(Note : 5/6 = 0.833)

Efficiency of A = 10%
Efficiency of B = 6.66%

∴ Required number of days = 100/16.66

Correct Option: D

Efficiency of A = 10%
Efficiency of B = 6.66%

∴ Required number of days = 100/16.66 = 6 days