Mrs Yeo left home at 10 a.m. and drove towards the city. 1¹₂ hour later, Mr Yeo left the house and drove at an average speed of 87 km/h towards the city. When Mr Yeo reached his destination at 2 p.m., Mrs Yeo was 16 km away from the city. Find Mrs Yeo’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 10 a.m. = 11.30 a.m.

Time that Mr Yeo left the house = 11.30 a.m.

Time that Mr Yeo took from 11.30 a.m. to 2 p.m. to reach his destination = 2 h 30 min

1 min = ¹₆₀ h
30 min = ³⁰₆₀ h = ¹₂ h
2 h 30 min = 2¹₂ h

Distance that Mr Yeo drove
= 2¹₂ x 87
= 217¹₂ km

Distance that Mrs Yeo drove when Mr Yeo reached
= 217¹₂ - 16 
= 201¹₂ km

Time that Mrs Yeo took to travel from 10 a.m. to 2 p.m. = 4 h

Mrs Yeo's average speed
= 201¹₂ ÷ 4
= 50³₈ km/h

Answer(s): 50³₈ km/h