The speed of the engine of a train is 150 km/hr. By connecting coaches to the engine its speed decreases. The decrease in speed is given by the function d=x^2+3x-2 (km/hr), where x is the number of coaches connected. Find the minimum speed ( in km/hr) with which the train can run?
1) 1
2 11
3) 22
4) 33
5) None of these
option 3
ReplyDelete22
max number of coaches =10
did by trial and error.
is there a better way of doing this , instead of just trial and error??
yupp there is
ReplyDeletecan u please share that method .
ReplyDeletelet others try at least, after that if no one gets it, i will post the solution
ReplyDeletefor the egine to push the train the speed should be greater than 0...
ReplyDeleteFinal speed of train= Speed of engine- decrease in speed.
At number of couches= 11 the decreease in speed = 121+33-2=152KMPH
this is not possible, decrease cannot be greater than 150...
so the number of Coachs has to be 10..with 10 d= 128KMPH
speed of train, with which it can run= 150-128=22...
Is this approach fine???
x^2+3x-2<150 is the limiting case
ReplyDeletesolving we get
x^2+3x-152=0
x=(-3+-sqrt(617)/2
so x comes approx 11
so x should be less than 11
so x=10
put x=10 we get 128
so speed ia 150-128-122