Lesson: When to use Combinations

Comment on When to use Combinations

ausm! thnx!! :)

Amazing explanation. Crisp and precise. I am glad that i found you guys for my prep.
greenlight-admin's picture

Glad you like it!

Hi!
In the second question listed (urch webpage) I couldn't see the question even after scrolling to bottom. Could you look into that?
Thanks
greenlight-admin's picture

Thanks for the heads up.
That site has had several problems recently, so I have deleted the link.

Cheers and thanks,
Brent

Combinations have always been terrible for me to understand. Thank you for the great explanation.

So how do we determine there are no different toppings, when the question states 3 different toppings which could be mushrooms, onions, pepperoni etc.
greenlight-admin's picture

You're referring to the question that starts 3:55 in the above video.

I'm not sure what you're asking when you say "So how do we determine there are no different toppings"

Can you please elaborate?

Cheers,
Brent

Superb explanation.

the problem -

How many 3 -digit number greater than 399 ending eith 5 or 7?

Kindly let me know if I can proceed as below steps:-
Let us take there are no restriction of 5 or 7 so
First digit - 6 ways
Second digit - 10 ways
Third digit - 10 ways.

So total no. of ways = 6 * 10 * 10 =600

Now let us assume the last digit is not filled by 5 or 7

so,
First digit - 6 ways
Second digit - 10 ways
Third digit - 8 ways.

So total no. of ways = 6 * 10 * 8 =480 ways.

Therefore no. ways the number greater than 399 and the last digit is 5 or 7 = 600 -480 = 120 ways
greenlight-admin's picture

You're referring to the question that starts at 5:10 in the above video.

Yes, that approach works perfectly. It requires some extra steps, but the important thing is that you got the correct answer. Nice work!

Cheers,
Brent

Thanks Brent

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