Mrs Chiam left home at 8 a.m. and drove towards the city. 1¹₂ hour later, Mr Chiam left the house and drove at an average speed of 90 km/h towards the city. When Mr Chiam reached his destination at 1 p.m., Mrs Chiam was 19 km away from the city. Find Mrs Chiam’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₂ h = ¹₂ x 60 = 30 min
1¹₂ = 1 h 30 min

1 h 30 min after 8 a.m. = 9.30 a.m.

Time that Mr Chiam left the house = 9.30 a.m.

Time that Mr Chiam took from 9.30 a.m. to 1 p.m. to reach his destination = 3 h 30 min

1 min = ¹₆₀ h
30 min = ³⁰₆₀ h = ¹₂ h
3 h 30 min = 3¹₂ h

Distance that Mr Chiam drove
= 3¹₂ x 90
= 315 km

Distance that Mrs Chiam drove when Mr Chiam reached
= 315 - 19 
= 296 km

Time that Mrs Chiam took to travel from 8 a.m. to 1 p.m. = 5 h

Mrs Chiam's average speed
= 296 ÷ 5
= 59¹₅ km/h

Answer(s): 59¹₅ km/h