Aptitude - Odd Man Out and Series - Discussion

Yes, It is 73.

If we solve like that:
43 - 41 = 2,
47 - 43 = 4,
53 - 47 = 6,
61 - 53 = 8,
71 - 61 = 10,
73 - 71 = 2.

So, that 73 makes an error for the exact difference between the given numbers so according to me, 73 is an answer .

Why not 73?

Read the answer properly, it say that except 81 all are prime number. To all genius.

81 is divisible by 9, so it isn't a prime number. 9x9=81. the rest of the numbers can not be divided into evenly without a remainder. For example 5 is a prime because if you divide it by 2 you will have a remainder. 5 is only divisible by 5 or by 1.

also stated above was the formula: tn= t(n-1)+2n
where n= 1,2,3,4,...etc.
and t= 41,43,47,53,...etc.

If you plug in the numbers it doesn't equal the 2nd term which is 43.
let t= 1st term 41
n= 1

Example with above formula:tn= 41(1-1)+2(1)
41(0)+2 = 2?
I do understand t+2n
41+2(1)= 43
43+2(2)= 47
47+2(3)= 53

I am not trying to be picky, I was really trying to understand.
thanks for the above solutions!

81 is the only one which is divisible by 3.

t = 41 + 2 * 1 = 43
t = 43 + 2 * 2 = 47
t = 47 + 2 * 3 = 53
t = 53 + 2 * 4 = 61
t = 61 + 2 * 5 = 71
t = 71 + 2 * 6 = 83.

In the given Series there 73 followed by 71, so the answer must be 73.

Answer 81 is correct. Because except 81, all other numbers are a prime number.

Yes, I agree with Sandeep Shenoy.

Why its ans can't be 47?

41 4>1
43 4>3
47 4<7
53 5>3
61 6>1
71 7>1
73 7>3
81 8>1

Every 10th digit no is more than except 47, so the answer is 47. Why this answer is wrong?