Student: In each series, look for the degree and direction of change between the numbers. In other words, do the numbers increase or decrease, and by how much?
Look at this series: 88, 3, 80, 12, __, 21 ... What number is missing?
Options:
(A) 72
(B) 78
(C) 68
(D) 30
(E) 70.
Another student: Let's say, hmmm...
A
72
This is an alternating addition and subtraction series. In the first pattern, 8 is subtracted from each number to arrive at the next. In the second, 9 is added to each number to arrive at the next. Final answer: (A).