Answer :
The factors that 213 and 405 share is 3 because the factors for 213 is 3 and 71 and the factors for 405 are 3,3,3,3 and 5 sooo....the answer to your question would be 3.......hope it helps :)
Let's factor the numbers into prime numbers:
213 = 3 x 71
71 is a prime number, so we can't simplify it down anymore.
405 = 5 x 81 = 5 x 3 x 3 x 3 x 3
So they have only 3 in common.
213 = 3 x 71
71 is a prime number, so we can't simplify it down anymore.
405 = 5 x 81 = 5 x 3 x 3 x 3 x 3
So they have only 3 in common.