Correct Answer: $\frac{160}{3}$ km/hr

Solution : According to the question,
the speed in the first 10 km is 40 km/hr.
⇒ Time taken in first 10 km (T ₁ ) = $\frac{\text{Distance}}{\text{Speed}}$ = $\frac{10}{40}$ hours
The time taken in the first 10 km is twice the time taken in the second 10 km:
So, the time taken in the second 10 km (T ₂ ) = $\frac{T1}{2}$ = $\frac{10}{40 × 2}$ hours
and the time taken in the fourth 10 km (T ₄ ) = T ₁ = $\frac{10}{40}$ hours
The time taken in the third 10 km (T ₃ ) is half of the time taken in the fourth 10 km:
⇒ T ₃ = $\frac{T4}{2}$ = $\frac{10}{40×2}$
Total time = T1 ​+ T2 ​+ T3​ + T4​​
= $\frac{10}{40}$ + $\frac{10}{40 × 2}$ × $\frac{10}{40 × 2}$ + $\frac{10}{40}$
= $\frac{2}{8}$ + $\frac{1}{8}$ × $\frac{1}{8}$ + $\frac{2}{8}$
= $\frac{6}{8}$
= $\frac{3}{4}$ hours
Now,
Average Speed = $\frac{\text{Total Distance​}}{\text{Total Time}}$
= $\frac{40}{\frac{3}{4}}$
= $\frac{40 × 4}{3}$ = $\frac{160}{3}$ km/hr
Hence, the correct answer is $\frac{160}{3}$ km/hr.