A petroleum refinery needs to empty a spherical storage tank of radius 9 m. The contents will be transferred to cylindrical tanks of radius 4 m and height 20 m. What is the minimum number of cylindrical
tanks that must be available in order to empty the entire spherical tank?

see explanation

step-by-step explanation:

since the sequence is geometric there is a common ratio r between consecutive terms, that is

r = 4 ÷ - 2 = - 2

r = - 8 ÷ 4 = - 2

r = 16 ÷ 8 = - 2

the next term - 13 must be incorrect as it should be - 32 for the sequence to be geometric.

the first 4 terms are therefore geometric with common ratio r = - 2