Math Problem (Level 1) : Difference of three clocks (D15)

Three clocks, A, B and C were set at noon of one day. 

When it was 6:00 p.m. by A, it was 5:50 p.m. by B In the same day. 

When it was 7:00 p.m. by B, it was 7:20 p.m. by C. 

When it is 11:00 p.m. by C of the day, find the time of A and B.




Answer
A : 10:48 p.m.   B : 10:30 p.m.

Solution
Because when A runs six hours, B runs five hours 50 minutes; the ratio of the speed of A and B is 6 hours : 5 5/6 hours = 36 : 35. 

Because when B runs seven hours, C runs seven hours 20 minutes; the ratio of the speed of B and C is 7 hours : 7 1/3 hours = 21 : 22.

Thus, when C runs 11 hours, B runs 11 × 21/22 = 10.5 hours. 

The time of B is 10:30.

When B runs 10.5 hours, A runs 10.5 × 36/35 = 10.8 hours.

The time of A is 10:48.