ICSE Class 10CISCE
Share
Notifications

View all notifications
Books Shortlist
Your shortlist is empty

If the Speed of an Aeroplane is Reduced by 40 Km/Hr, It Takes 20 Minutes More to Cover 1200 Km. Find the Speed of the Aeroplane. - ICSE Class 10 - Mathematics

Login
Create free account


      Forgot password?

Question

If the speed of an aeroplane is reduced by 40 km/hr, it takes 20 minutes more to cover 1200 km. Find the speed of the aeroplane.

Solution

Let the original speed of the aeroplane be x km/hr.

Time taken to cover a distance of 1200 km = 1200/x  hrs

`("Time" = "Distance"/"Speed")`

Let the new speed of the aeroplane be (x - 40) km/hr

Time taken to cover a distance of 1200 km = `1200/(x - 40)` hrs

From the given information we have

`1200/(x - 40) - 20/60 = 1200/x`

`1200/(x - 40) - 1200/x = 20/60`

`(1200x - 1200x + 48000)/(x(x - 40)) = 1/3`

x(x - 40) = 48000 x 3

`x^2 - 40x - 144000 = 0`

`x^2 - 400x + 360x - 144000 = 0`

x(x - 400) + 360(x - 400) = 0

(x - 400)(x + 360) = 0

x = 400,-360

But, speed cannot be negative. So, x = 400.

Thus, the original speed of the aeroplane is 400 km/hr.

 

  Is there an error in this question or solution?

APPEARS IN

 Selina Solution for Selina ICSE Concise Mathematics for Class 10 (2018-2019) (2017 to Current)
Chapter 6: Solving (simple) Problems (Based on Quadratic Equations)
Ex.6C | Q: 3
Solution If the Speed of an Aeroplane is Reduced by 40 Km/Hr, It Takes 20 Minutes More to Cover 1200 Km. Find the Speed of the Aeroplane. Concept: Quadratic Equations.
S
View in app×