13. 1,6
18. -15,12
19. -7, 1/2
When you multiply two numbers which have the same sign the answer is positive. Therefore multiply eight and three to get 24 and the answer is positive; therefor the answers 24.
M1 = m4 = 50 (A) is the answer
Notice the following pattern:
2 - 0 = 2
6 - 2 = 4
12 - 6 = 6
20 - 12 = 8
It's reasonable to assume that consecutive terms in the sequence differ by increasing multiples of 2, so that for the next number (call it x) we expect to see
x - 20 = 10 ==> x = 30
and for the number after that (call it y) we would see
y - x = y - 30 = 12 ==> y = 42
