Time and Work Easy Level

LCM method: job = 30 units

A = 3 units a day, B = 2 units a day

Together = 5 units a day

Days = 30 ÷ 5 = 6

Trap: averaging 10 and 15 gives 12.5.

Answer: 6 days

Job = 24 units; A = 2, B = 1 a day

Together = 3 a day

Days = 24 ÷ 3 = 8

Answer: 8 days

B's rate = 1/12 − 1/20 = (5 − 3)/60 = 1/30

B alone = 30 days

Trap: 20 − 12 = 8 subtracts days, not rates.

Answer: 30 days

A = 2 units a day, B = 1 → together 3

Job = 3 × 18 = 54 units

A alone = 54 ÷ 2 = 27 days

Trap: 54 days is B alone.

Answer: 27 days

A alone = 20 days; B alone = 30 days

Job = 60 units; A = 3, B = 2 a day

Days = 60 ÷ 5 = 12

Answer: 12 days

A did 5/15 = 1/3 → 2/3 left

B does 2/3 in 12 days

B alone = 12 × 3/2 = 18 days

Answer: 18 days

Job = 60 units; rates 6, 5, 4 → 15 a day

Days = 60 ÷ 15 = 4

Answer: 4 days

Job = 60 units; A+B = 6, B+C = 4, C+A = 5 a day

Adding: 2(A + B + C) = 15 → A + B + C = 7.5

Days = 60 ÷ 7.5 = 8

Answer: 8 days

All three = 1/8 a day

A = 1/8 − (B + C) = 1/8 − 1/15 = 7/120

A alone = 120/7 = 17 1/7 days

Answer: 17 1/7 days

Rates A : B = 5 : 4 → times A : B = 4 : 5

A = 25 × 4/5 = 20 days

Trap: 18.75 takes 25% off the time.

Answer: 20 days