Mark took 6 hours to travel from Country K to Country L at 50 km/h. Then he travelled from Country L to another country at 1.5 times his original speed. 70% of the distance from Country K to Country L is equal to ¹₅ of the distance from Country L to the next country. Find the average speed for the whole journey and express it as a mixed number.
Distance he travelled from Country K to Country L
= 6 x 50
= 300 km

Speed from Country L to another country
= 1.5 x 50
= 75 km/h

70% = ⁷⁰₁₀₀ = ⁷₆

⁷₁₀ Distance from Country K to Country L = ¹₅ Distance from Country L to next country
⁷₁₀ Distance from Country K to Country L = ⁷₃₅ Distance from Country L to next country

10 u = 300
1 u = 300 ÷ 10 = 30

Distance from Country L to the next country
= 35 u
= 35 x 30
= 1050 km

Time taken from Country L to the next country
= 1050 ÷ 75
= 14 h

Total distance of the whole journey
= 300 + 1050
= 1350 km

Total time taken for the whole journey = 6 + 14 = 20 h

Average speed of the whole journey
= 1350 ÷ 20
= 67 ¹⁰₂₀
= 67 ¹₂ km/h

Answer(s): 67 ¹₂ km/h