Mrs Chau left home at 9 a.m. and drove towards the city. 2⁵₆ hour later, Mr Chau left the house and drove at an average speed of 101 km/h towards the city. When Mr Chau reached his destination at 3 p.m., Mrs Chau was 18 km away from the city. Find Mrs Chau’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
⁵₆ h = ⁵₆ x 60 = 50 min
2⁵₆ = 2 h 50 min

2 h 50 min after 9 a.m. = 11.50 a.m.

Time that Mr Chau left the house = 11.50 a.m.

Time that Mr Chau took from 11.50 a.m. to 3 p.m. to reach his destination = 3 h 10 min

1 min = ¹₆₀ h
10 min = ¹⁰₆₀ h = ¹₆ h
3 h 10 min = 3¹₆ h

Distance that Mr Chau drove
= 3¹₆ x 101
= 319⁵₆ km

Distance that Mrs Chau drove when Mr Chau reached
= 319⁵₆ - 18 
= 301⁵₆ km

Time that Mrs Chau took to travel from 9 a.m. to 3 p.m. = 6 h

Mrs Chau's average speed
= 301⁵₆ ÷ 6
= 50¹¹₃₆ km/h

Answer(s): 50¹¹₃₆ km/h