A. 103
B. 105
C. 110
D. 112
E. 115

Answer: A

Explanation:
Assuming total distance travelled = 2x kilometres
Time taken for the first “x” kilometres = \frac{x}{90hours}
Time taken for the second half = \frac{x}{120 hours}
Average speed = \frac{Total distance}{Total time taken}
So, Average speed = \frac{2x}{\frac{x}{90}+\frac{x}{120}} = \frac{720}{7} = 102.8 kmph
Closest answer is 103 kmph.
Shortcut:
If the distance traveled is constant, then the average speed = \frac{2ab}{a+b}
Where “a” and “b” are two different speeds.
\frac{2ab}{a+b}=\frac{2*90*120}{210}=\frac{21600}{210} = 102.8 kmph
Closest answer is 103 kmph.
Hence the answer is A.

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