Geometric progression

Question

a drilling machine is designed to have 6 speeds ranging from 100 rpm to 800 rpm. if it is known that the speeds from a geometric progression, determine their values to the nearest whole number.

Answer 1

The speeds are:  100, A, B, C, D, 800 rpm     [there are 6 speeds]

 

In a geometric progression, each term is the product of the previous term and a common ratio (r).  So, the sequence is:

  A          Ar          Ar²      Ar³       At⁴      Ar⁵ 

 100       100r      100r²  100r³   100r⁴    800

 

 

This gives us:     100r⁵ = 800

                           r⁵ = 8

                           r = 1.5156

 

The speeds are:

100    152   230   348   528    800      rpm