Student: 5,9,19,31,51,__
Options:
(A) 84
(B) 80
(C) 81
(D) 82
(E) 83.
Another student: Let's say, hmmm...
(9+5) +5 = 19
(16+9) +6 = 31
(28+16)+7 = 51
(48+28)+8 = 84 Final answer: (A).