Exercise 4.1 Q2 - 4 | Class 10| Chapter 4 | Quadratic Equations| CBSE

Added: 2026-05-17

[00:00:00]Final question is here the question is a train travels a distance of 480 km at a uniform speed.

[00:00:06]So the distance is 480 km.

[00:00:08]Distance is equals to 480 km.

[00:00:12]If the speed had been 8 km less, then it would have taken 3 hours more to cover the same distance. So if the speed will decrease, the kilometers the speed will decrease, then the time will automatically increase. Which We need to find the speed of the train.

[00:00:25]What is the speed of the train? Let speed be X.

[00:00:29]X be the speed, then we will write it as What is the formula? Distance is equals to speed into time.

[00:00:34]What is the distance here? 480 km is equals to speed into time. Speed is X into T is the actual time it will taken to in an average speed.

[00:00:43]So time is equals to 480 divided by X.

[00:00:46]This is the actual time.

[00:00:47]Now we will It was given in the question that if the speed had been decreased.

[00:00:52]Okay, now we will write it as distance is equals to speed into time. If distance is 480 km, speed is decreased by 8 km/h, which means X minus 8. The speed is X and it was decreased by 8. So we will write it as X minus 8 into and the time is increased 3 hours, which means T plus 3.

[00:01:10]This is the way we will write. Now, what is the three T plus three value here?

[00:01:14]480 divided by X minus 8. And we already know what is the T value. Original value is 480 I will write it here. 480 divided by X plus 3 is equals to Here we are substituting the T value.

[00:01:27]What is the T value? 480 divided by X.

[00:01:29]After substituting I'll get 480 divided by 480 divided by X plus 3 is equals to 480 divided by X minus 8. Now take the LCM. 480 plus 3X divided by X is equals to 480 divided by X minus 8. Now cross multiply each other.

[00:01:46]X minus 8 into 480 plus 3X is equals to 480 into X 480X. Now we will multiply each other.

[00:01:57]X minus 8. That's it. X into 480 480X plus 3 X into 3X 3X squared minus 480 into 8 8 zeros are zero 8 8s are 64 8 4s are 32 plus 6 38 40 minus 8 8 3s are 24X is equals to 480X.

[00:02:17]Okay, we will write it directly here.

[00:02:19]Minus 480X is equals to zero. Here plus 480X minus 480X cancel. Finally, we'll get 3X squared minus 24X minus 3840 is equals to zero. Now, if I take three as common what will I get? X squared minus 38X minus 1280 is equals to zero. Finally, we got X squared minus 8X minus 1280 is equals to zero. This is the quadratic equation we found. Here, the speed is X.

[00:02:47]So, we find both.

[00:02:48]Full video link is in the description.

[00:02:50]Thank you. This is Sunehra signing off.