Two numbers are said to be 'relatively prime' if their greatest common factor is 1. How many integers greater than 10 and less than 30 are relatively prime with 28?

a. 6 integers

b. 4 integers

c. 8 integers

d. 9 integers

d. 9 integers

Step-by-step explanation:

Given that two numbers are said to be 'relatively prime' if their greatest common factor is 1.

We are to find relatively prime with 28 which are greater than 10 and less than 30

We have 11,12,13 ... 29 satisfying the criteria greater than 10 and less than 30

To be relatively prime with 28, common factors should be only 1.

28 = 2x2x 7. Hence the numbers which do not have factors as 2 or 7 will be relatively prime. Remove all the even numbers from the list.

We have 11,13,15 ... 29.

Of these 21 is the multiple of 7 so remove that.

Thus we have now 11,13,15,17,19,23,25,27,29

9 integers

d. 9 integers