to be the coprime no. greater than 10 which number should be present on undit place
Answers
The last digit can’t be even (0,2,4,60,2,4,6 and 88) otherwise the whole number is even (proof: for one digit numbers it is obvious and numbers with more digits the are of the form 10x+e∣x∈N110x+e∣x∈N1 with ee as the last and if ee is even then e2e2 is whole number so 5x+e25x+e2 is too) or 55 (because any number with 55 in the end is a multiple of 55), so the odd digits remaining are:
11 (example primes: 11,31,41,61,71,…11,31,41,61,71,…)
33 (example primes: 3,13,23,43,53,73,83,…3,13,23,43,53,73,83,…)
77 (example primes: 7,17,37,47,67,97,…7,17,37,47,67,97,…)
99 (example primes: 19,29,59,79,89,…19,29,59,79,89,…)
12 ANSWERS
Abishek Kannappan
Answered Jul 18, 2017
There are ten digits: 0,1,2,3,4,5,6,7,8,9
All integers with 0 in the ones place are multiples of 10, so we can rule out 0.
1 can be in the ones place, as 11 is a prime number.
All integers with 2 or a multiple of 2 in the ones place are even and therefore multiples of 2, so we can rule out 2, 4, 6, and 8.
3 can be in the ones place, as 13 is a prime number.
All integers with 5 in the ones place are multiples of 5, so we can rule out 5.
7 can be in the ones place, as 17 is a prime number,
9 can be in the ones place, as 19 is a prime number.
Therefore, the possible ones-place digits of a prime greater than 10 are: 1,3,7,9