Question

How many four digits number can be formed with the digits 3,5,7,8,9 which are greater then 7000 if repetition of digits are not allowed?

Answer 1

Answer:

Step-by-step explanation:

Being greater than 7000 means it must start with 7,8 or 9. So we have 3 options here.

For the second digit we have 4 options, because we can’t repeat the one we used as first digit.

For the third digit we have 3 options.

And for the last digit we have 2 options.

So, we have a total of 3×4×3×2=72 numbers of four digits.

Answer 2

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Given,

" Repetition of given digits is not allowed "

Thus,

The first place can be filled in 3 ways by anyone of 7 , 8 and 9 digits

The second palce can be filled in 4 ways by anyone of the remaining digits

The third palce can be filled in 3 ways by anyone of the remaining digits

The fourth palce can be filled in 2 ways by anyone of the remaining digits

By multiplication principle , we get

Number of four digits numbers greater than 7000 = 3 × 4 × 3 × 2 i.e 72 ways

Hence , the required number of four digits numbers which are greater than 7000 is 72