00:00Welcome everyone. So yes, a lot of people thought that the answer for this one is supposed to be 1 upon 17 because 9 minus 8 is 1. 9 plus 8 is 17. Okay, but that's not how these things work. Please understand it is not just 9, it is 9 factorial and 8 factorial.
00:16So when you have something like this, let's understand what is 9 factorial. It is an expansion of products of all the integers in the decreasing order until and unless you reach the value of 1. Okay, so similarly for 8 factorial, it would be what?
00:368 multiplied by 7 multiplied by 6 multiplied by 5 multiplied by 4 multiplied by 3 multiplied by 2 multiplied by 1. So I can write 9 factorial as nothing but what? 9 multiplied by 8 factorial.
00:52So you can write this as what? 9 into 8 factorial minus 8 factorial upon 9 into 8 factorial plus 8 factorial. So 8 factorial we have to take common and 9 minus 1 upon 8 factorial 9 plus 1.
01:13So this is getting cancelled and 9 minus 1 is what? 9 plus 1 is what? 10. So we can reduce this further. This has become 4 upon 5. I hope this is very very clear to everyone. That's it for today. I will see you in the next video.
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