Astudent is required to work exactly ten problems from a twenty-problem exam. in how many ways can the problems be chosen?

10 out of 20 ways

Step-by-step explanation:

If he has to work exactly 6 out of 10 and 3 out of the first 4, then he must work exactly 3 out of the last 6. Hence, the answer to this question is to be found in the sum of the number of ways to select 3 things from 4 things plus the number of ways to select 3 things from 6 things:

You can do your own arithmetic.

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jml angle lkj & angle mj = lm