Justin took 4 hours to travel from Country B to Country C at 50 km/h. Then he travelled from Country C to another country at 1.8 times his original speed. 60% of the distance from Country B to Country C is equal to ¹₆ of the distance from Country C to the next country. Find the average speed for the whole journey and express it as a mixed number.
Distance he travelled from Country B to Country C
= 4 x 50
= 200 km

Speed from Country C to another country
= 1.8 x 50
= 90 km/h

60% = ⁶⁰₁₀₀ = ³₄

³₅ Distance from Country B to Country C = ¹₆ Distance from Country C to next country
³₅ Distance from Country B to Country C = ³₁₈ Distance from Country C to next country

5 u = 200
1 u = 200 ÷ 5 = 40

Distance from Country C to the next country
= 18 u
= 18 x 40
= 720 km

Time taken from Country C to the next country
= 720 ÷ 90
= 8 h

Total distance of the whole journey
= 200 + 720
= 920 km

Total time taken for the whole journey = 4 + 8 = 12 h

Average speed of the whole journey
= 920 ÷ 12
= 76 ⁸₁₂
= 76 ²₃ km/h

Answer(s): 76 ²₃ km/h