2nd digit is the smallest
so it must be 1.

3rd digit is the largest
so it can be 9 and the first digit is 8.

1st digit is greater than the
addition of 4th and 5th digit.
so it can be 1 2;2 1;3 4;4 3;2 3;3 2;2 4;4 2 but 5th digit is between the 1st and 2nd digit and half of the 4th digit so it can be 4 and 2 and so we should have 1 more prime no.

so the third digit cannot be 9 it should be 8 and the first digit is 7.

so the number is 71842.

why cant it be 70842? if i consider 0 as the smallest number?

70821 is also possible

1)7 2 only 2 prime nos 0 is not considered as prime as divisible by any number with remainder 0

2)1st digit 7 is 1 less than 3rd i e 8

3)3rd digit is largest 8

4)1st digit 7> sum of 4th and 5th i e 2+1 3

5)5th digit 1 is between 1st and 2nd i e betn 7 and 0

6)2nd digit is smallest i e 0