Mrs Ang left home at 7 a.m. and drove towards the city. 1¹₂ hour later, Mr Ang left the house and drove at an average speed of 82 km/h towards the city. When Mr Ang reached his destination at 3 p.m., Mrs Ang was 30 km away from the city. Find Mrs Ang’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 7 a.m. = 8.30 a.m.

Time that Mr Ang left the house = 8.30 a.m.

Time that Mr Ang took from 8.30 a.m. to 3 p.m. to reach his destination = 6 h 30 min

1 min = ¹₆₀ h
30 min = ³⁰₆₀ h = ¹₂ h
6 h 30 min = 6¹₂ h

Distance that Mr Ang drove
= 6¹₂ x 82
= 533 km

Distance that Mrs Ang drove when Mr Ang reached
= 533 - 30 
= 503 km

Time that Mrs Ang took to travel from 7 a.m. to 3 p.m. = 8 h

Mrs Ang's average speed
= 503 ÷ 8
= 62⁷₈ km/h

Answer(s): 62⁷₈ km/h