Aptitude - Time and Distance - Discussion
Discussion Forum : Time and Distance - General Questions (Q.No. 6)
6.
In a flight of 600 km, an aircraft was slowed down due to bad weather. Its average speed for the trip was reduced by 200 km/hr and the time of flight increased by 30 minutes. The duration of the flight is:
Answer: Option
Explanation:
Let the duration of the flight be x hours.
| Then, | 600 | - | 600 | = 200 |
| x | x + (1/2) |
 |
600 | - | 1200 | = 200 |
| x | 2x + 1 |
x(2x + 1) = 3
2x2 + x - 3 = 0
(2x + 3)(x - 1) = 0
x = 1 hr. [neglecting the -ve value of x]
Discussion:
210 comments Page 12 of 21.
Arun said:
1 decade ago
@Ravi, 200 is not the avg speed, it says average speed is reduced by 200, not to 200.
Jay said:
1 decade ago
Here A Shortcut method.
Initial speed = 600km/hr = s1.
Final Speed = 600-200 = 400km/hr = s2.
So, (Taking ratio of speed),
s1 : s2 = 600 : 400= 3 : 2.
So, time taken,
t1 : t2 = 2 : 3 (time and speed inversely proportional).
1 part time= 30 min.
So t1= 2*30 = 60 min = 1hr.
Initial speed = 600km/hr = s1.
Final Speed = 600-200 = 400km/hr = s2.
So, (Taking ratio of speed),
s1 : s2 = 600 : 400= 3 : 2.
So, time taken,
t1 : t2 = 2 : 3 (time and speed inversely proportional).
1 part time= 30 min.
So t1= 2*30 = 60 min = 1hr.
Rahim Shaikh said:
1 decade ago
Another method:
let x = original speed.
And y= original time taken.
So 600/x=y--------(1).
Now we know if speed reduces 30 minutes more will be taken.
i.e 30/60 hours.
So,
600/x-200= y+30/60 here 30/60 means 30 minutes.
Now put the value of y as shown in (1),
So equation will be,
600/x-200= 600/x - 30/60.
You will get,
x2-200x-240000=0 here x2 means x square.
(x-600)(x+200) = 0.
X = 600.
That's why
Time =600/600.
=1 hours.
Hope you guys understand
let x = original speed.
And y= original time taken.
So 600/x=y--------(1).
Now we know if speed reduces 30 minutes more will be taken.
i.e 30/60 hours.
So,
600/x-200= y+30/60 here 30/60 means 30 minutes.
Now put the value of y as shown in (1),
So equation will be,
600/x-200= 600/x - 30/60.
You will get,
x2-200x-240000=0 here x2 means x square.
(x-600)(x+200) = 0.
X = 600.
That's why
Time =600/600.
=1 hours.
Hope you guys understand
Khrish said:
1 decade ago
Suppose duration of flight is = x.
Speed = distance/time.
200=(600/x)-(600/(x+30mins)).
200=(600/x)-[600/(x+(30/60)hr)].
200=(600/x)-[600/(x+(1/2))].
200=(600/x)-[600/((2x+1)/2)] by LCM,
200=(600/x)-[1200/2x+1].
200=600[(1/x)-(2/2x+1)].
200/600=(1/x)-(2/2x+1).
1/3=(2x+1-2x)/(2x^2+x).
1/3=1/(2x^2+x).
2x^2+x-3=0.
(2x+3)(x-1)=0.
X=-3/2, x=1.
I hope you got it...;).
Speed = distance/time.
200=(600/x)-(600/(x+30mins)).
200=(600/x)-[600/(x+(30/60)hr)].
200=(600/x)-[600/(x+(1/2))].
200=(600/x)-[600/((2x+1)/2)] by LCM,
200=(600/x)-[1200/2x+1].
200=600[(1/x)-(2/2x+1)].
200/600=(1/x)-(2/2x+1).
1/3=(2x+1-2x)/(2x^2+x).
1/3=1/(2x^2+x).
2x^2+x-3=0.
(2x+3)(x-1)=0.
X=-3/2, x=1.
I hope you got it...;).
Kush said:
1 decade ago
Why there is always subtraction in the formula?
i.e. 600/x - 600/(x+.5) = 200.
Why "-" ?
i.e. 600/x - 600/(x+.5) = 200.
Why "-" ?
Dinesh said:
1 decade ago
2x^2+x-3=0 how to solve this factorisation? So please help me.
Nandasena said:
1 decade ago
It is said that average speed is reduced by 200. Not just speed is reduced by 200. Then we know there is another equation to calculate average speed. But in here it has not used. Can someone please explain?
Ramesh said:
1 decade ago
Why the difference in speed matched with 200km/hr?
Khushbu said:
1 decade ago
@Avy.
In equation (2x-3)(x+1) =0.
Then x=3/2 and x = -1.
So how x=1?
In equation (2x-3)(x+1) =0.
Then x=3/2 and x = -1.
So how x=1?
Ranjith said:
1 decade ago
You have done a mistake in this.
400x2+200x-600=0.
4x2 + 2x - 6= 0.
2x2 + x - 3 = 0.
2x2 - 2x + 3x - 3 = 0.
2x (x - 1) + 3 (x- 1) = 0.
(2x + 3) (x - 1) = 0.
x=3/2 or x=1.
It is (x-1)=0 and not (x+1)=0....
So that while equaling this we get as,
x=1...
Hoping you understand now.
400x2+200x-600=0.
4x2 + 2x - 6= 0.
2x2 + x - 3 = 0.
2x2 - 2x + 3x - 3 = 0.
2x (x - 1) + 3 (x- 1) = 0.
(2x + 3) (x - 1) = 0.
x=3/2 or x=1.
It is (x-1)=0 and not (x+1)=0....
So that while equaling this we get as,
x=1...
Hoping you understand now.
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers