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## Comment on

When to use Combinations## ausm! thnx!! :)

## Amazing explanation. Crisp

## Glad you like it!

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

## Thanks for the heads up.

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

## So how do we determine there

## You're referring to the

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

## You're referring to the

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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