Julian took 4 hours to travel from Country A to Country B at 50 km/h. Then he travelled from Country B to another country at 1.6 times his original speed. 40% of the distance from Country A to Country B is equal to ¹₅ of the distance from Country B to the next country. Find the average speed for the whole journey and express it as a mixed number.
Distance he travelled from Country A to Country B
= 4 x 50
= 200 km

Speed from Country B to another country
= 1.6 x 50
= 80 km/h

40% = ⁴⁰₁₀₀ = ²₄

²₅ Distance from Country A to Country B = ¹₅ Distance from Country B to next country
²₅ Distance from Country A to Country B = ²₁₀ Distance from Country B to next country

5 u = 200
1 u = 200 ÷ 5 = 40

Distance from Country B to the next country
= 10 u
= 10 x 40
= 400 km

Time taken from Country B to the next country
= 400 ÷ 80
= 5 h

Total distance of the whole journey
= 200 + 400
= 600 km

Total time taken for the whole journey = 4 + 5 = 9 h

Average speed of the whole journey
= 600 ÷ 9
= 66 ⁶₉
= 66 ²₃ km/h

Answer(s): 66 ²₃ km/h