1.

Sitesh drove 12 hours at a speed of @ 75 km/hr. At present, how long should he drive at a speed of @ 90 km/hr so that the overall average speed will be 81 km/hr?1. 92. 7.53. 84. 6

Answer» Correct Answer - Option 3 : 8

Given :

Sitesh drove 12 hours at a speed of @ 75 km/hr

Concept used :

Average speed = Total distance/Total time 

Calculations :

Let the time taken for 90 km/h be 'x' 

Total distance = 75 × 12 + 90 × x 

⇒ 900 + 90x 

Total time = (12 + x) hours 

According to the question 

The overall average speed is 81 km/h then, 

81 = (900 + 90x)/(12 + x) 

⇒ 81 × (12 + x) = 900 + 90x 

⇒ x = 8 

∴ He drove for 8 hours at the speed of 90 km/h

 



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