Explanation

Now here we have digits 3,4 and 8. How many ways can we arrange them to form a three digit number.

Lets pick one digit at a time.

1st Digit -> 3 Possibilities
2nd Digit -> 2 Possibilities
3rd Digit -> 1 Possibility

Number of digits = \(3 \times 2 \times 1 =6.\)

Hence option B is correct


The other way to solve it is to write out the possible three-digit positive integers and count them: 348, 384, 438, 483, 834, 843 → 6 three-digit positive integers While this method is efficient when the question only has three digits, it can get quite complicated with more digits or four-digit positive integers.


Note this is applicable for the statement:
How many ways can n distinct things be arranged? Answer: \(n!\)
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Normally you would have a point there, however, the question states 'three digits are' implying that all three digits exist in the number and since there are only 3 places there is no scope for repetition.

If the question was formatted as 'total number of 3 digit numbers formed by using 3, 4 and 8' then repetition is a definite possibility.

Paying attention to the language of the questions in the GRE is extremely important.

Hope this helps.
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Sandy
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