# What is the value of n?

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If 2nC4: nC3 = 21:1, then find the value of n.

please note that this is a permutation combination question.

If 2nC4: nC3 = 21:1, then find the value of n.

please note that this is a permutation combination question.

##### 1 Answer

#### Explanation:

Notice a few things.

and

Putting this all together we have

We want

Quadratic formula tells us that

So

Since