Aptitude - Odd Man Out and Series - Discussion

It will definitely 73.

Thank you ankita.

Hey people it should be 73 also..... because in each case 2 is getting added and in that case 73 doesn't fit!!

What is prime no?

4*10+1, 7*6+1, 6*8-1, 6*9-1, 6*10+1, 7*10+1, 8*9+1,
but there are 9*9= 81

I am not agree with Vikash and ankita as according to them 73 and 81 both will be the answer.But we have to choose one answer.So correct answer is 81 which is not a prime number

All the numbers are prime numbers except 81.

Prime number series is 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997 etc.

Hey how you express above formula in to the sum. tn=t (n-1) +2n.
For example =41 (1-1) +2*1=2.

41+2=43.
43+4=47.
47+6=53.
53+8=61.
61+10=71.
71+2=73.
73+4=77.
But there is 83, which was not in same sequence. There must be 77.

A number which is divisible by one (i.e 1) and itself (the same number that is given) is called a prime number.