how many 5 digits telephone number can be constructed using the digits 0 to 9 if each number starts with 67 and number digit appears more than once
Answers
Answered by
3
Answer:
the answer is 729.
Step-by-step explanation:
here we use combination.
so total 5 digit no.
_ _ _ _ _
where first two digits are 67
so the remaining three digits are with repeating values are
6 7 _ _ _
= 9×9×9
= 729 ans.
Answered by
4
Answer: 336
Explanation;
Total number of digits = 10 i.e., (0, 1, 2, 3,.... , 9)
Now. since each number has to start with 67, thus first two digits of 5 digit number are fixed. We are then left with 8 digits which are to be used to fill up 3 vacant places.
So,Third digit can be selected in 8 ways, fourth digit can be selected in 7 ways and fifth digit can be selected in 6 ways.
So,Total 5 digit numbers that can be constructed = 8 x 7x6 = 336.
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