Answer:
An arithmetic sequence, The difference in any term with the previous term is same.
Explanation:
See, ah this is a little bit easy question so let’s start solving it -:
Firstly, um see the difference between the given numbers-: 1, 3, 5, 7,9 _?
Between 1 and 3 the difference is 2
Between 5 and 3 the difference is 2
Between 7 and 5 the difference is 2
Between 9 and 7 the difference is 2
So, here we see the difference among all is same. So. it is an arithmetic sequence.
So, let's find the fourth term. We can either do it by arithmetic progression or by simply adding 2 to 7. I.ll first show you by doing A.P. then we will check the answer by adding 2 to 7.
So, as we know the basic formula of A.P. which is -: a1+(n-1)d
Here, a1=1, n=5, d=2
Let’s put the values in the formula-: 1+(5–1)2 = 1+(4)2 = 1+8 = 9
Now let’s check it. As the difference between each digit is same so definately the difference between 9 and the unknown number is 2.
Then, the unknown no. is 9+2 = 11
Hence, the answer is 11