It is increasing by 4 and the nth term is 4n+1
3, 13, 17, 23 are prime numbers. The others are not.
Mode is the most frequent. Sorting to make it easier to see the frequency of the numbers: {13, 16, 17, 21, 25, 25, 30} - 25 appears twice and every other number once. Thus: mode of the numbers is 25.
Arithmetic
Assuming the pattern would continue: 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13...
It is increasing by 4 and the nth term is 4n+1
3, 13, 17, 23 are prime numbers. The others are not.
You have to find a pattern in the numbers, and exclude the one that messes up the pattern.
5, 13 and 17 are prime.
Mode is the most frequent. Sorting to make it easier to see the frequency of the numbers: {13, 16, 17, 21, 25, 25, 30} - 25 appears twice and every other number once. Thus: mode of the numbers is 25.
Arithmetic
Assuming the pattern would continue: 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13...
13/15 = 65/75 21/25 = 63/75 13/15 is bigger.
11, 13, 15, 17, 19, 21, 23
They are all prime numbers except for 15 21 25 and 27 which are composite numbers
25 + 16 - 13 - 21 = 7
17/25 is greater.