Question

The speed of a plane was raised by 60% by the pilot and then the raised speed was reduced by 50%. The speed measured by the sonic radar at this point of time was 2400 km/h. Find the initial speed of the plane. 
1. 3000 km/h 
2. 2800 km/h 
3.  2400 km/h 
4. 3200 km/h 

Answer 1

Correct Answer - Option 1 : 3000 km/h 

Given,

Speed is raised by 60%

Then reduced by 50%

Current speed = 2400 km/hr

To find,

The initial speed of the plane.

Solution,

We can simply solve this mathematical problem by using the following mathematical process.

Let, the initial speed = x km/hr

Speed after increasing = x + (x × ( 60 / 100 ) ) = x + ( 3x / 5 ) = 8x / 5 km/hr

Speed after decreasing = ( 8x / 5 ) - ( ( 8x / 5 ) ×  ( 50 / 100) ) = ( 8x / 5 ) - ( 4x / 5 ) = 8x - ( 4x / 5) = 4x / 5 km/hr

According to the data mentioned in the question,

4x / 5 = 2400

x = 2400 × ( 5 / 4 )

x = 3000

∴ The initial speed was 3000 km/hr