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Solutions
The correct answer is Option 3 i.e. 41 km.
Concept:- If a person covers a distance in t hours, with the speed of p km/hr in the first half and with the speed of q km/hr in the second half, then the total distance D covered by him is
D = 2 × t × (p × q)/(p + q)
Now, according to the question
Distance covered by Arpit
D1 = 2 × 3.5 × (12 × 15)/(12 + 15)
⇒ D1 = 1260/27
⇒ D1 = 46.66 or 47 km
Distance covered by Arpita
D2 = 2 × 4 × (18 × 20)/(18 + 20)
⇒ D2 = 2880/38
⇒ D2 = 75.78 or 76 km
Total distance = D1 + D2 = 47 + 76 = 123
one third of 123 = 1/3 × 123 = 41 km