In a geometric sequence, u find the next term by multiplying by the common ratio (r), which in this problem = 0.5
A1....means first term
so the first term is 40
second term would be 40 0.5 = 20
third term is 20 0.5 = 10
fourth term is 10 * 0.5 = 5
so ur first 4 terms are : 40, 20, 10, 5
