Ahmad took 5 hours to travel from Country C to Country D at 50 km/h. Then he travelled from Country D to another country at 1.5 times his original speed. 50% of the distance from Country C to Country D is equal to ¹₆ of the distance from Country D to the next country. Find the average speed for the whole journey and express it as a mixed number.
Distance he travelled from Country C to Country D
= 5 x 50
= 250 km

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

50% = ⁵⁰₁₀₀ = ¹₅

¹₂ Distance from Country C to Country D = ¹₆ Distance from Country D to next country
¹₂ Distance from Country C to Country D = ¹₆ Distance from Country D to next country

2 u = 250
1 u = 250 ÷ 2 = 125

Distance from Country D to the next country
= 6 u
= 6 x 125
= 750 km

Time taken from Country D to the next country
= 750 ÷ 75
= 10 h

Total distance of the whole journey
= 250 + 750
= 1000 km

Total time taken for the whole journey = 5 + 10 = 15 h

Average speed of the whole journey
= 1000 ÷ 15
= 66 ¹⁰₁₅
= 66 ²₃ km/h

Answer(s): 66 ²₃ km/h