Three digits are formed in 0,1,2,4,5,6 and 7 if digits os not repeated ? How many are the numbers
1 Answer
Apr 21, 2018
If the numbers starting with 0 are valid, 210. If not, 180.
Explanation:
If we take 3 digits at a time and form the numbers that result, the numbers starting with 0 will be valid (and so 12, which starts with 0, is as equally valid as 765). And so we can take the permutation of the population of 7 (note that there's no 3) taken 3 at a time gives:
If, however, we say that the numbers must be 3-digits long (thus implying numbers starting with 0 aren't allowed), then we have a situation where there are only 6 possibilities for the first digit (exclude the 0), but there are still 6 and 5 possibilities for the 2nd and 3rd digits:
