Aptitude Hack#8(3-3-19)

Question:

 A political party orders an arch for the entrance to the ground in which the annual convention is being held. The profile of the arch follows the equation y = 2x – 0.1x2 where y is the height of the arch in meters. The maximum possible height of the arch is

A)8 meters
B)10 meters
C)12 meters
D)14 meters

Answer: B)10 meters

 Explanation: 

y = 2x – 0.1x2 
dy/dx = 2 - 0.2x
 So the value maximizes at 2 - 0.2x = 0
 => x = 10 meters
 => y = 20 - 10 = 10 meters