Question

Which term of the progression 0.004, 0.02, 0.1, …. is 12.5?

Answer 1

By using the formula,

T_n = ar^n-1

Given:

a = 0.004

r = t₂/t₁ = (0.02/0.004)

= 5

T_n = 12.5

n = ?

So, T_n = ar^n-1

12.5 = (0.004) (5)^n-1

12.5/0.004 = 5^n-1

3000 = 5^n-1

5⁵ = 5^n-1

5 = n-1

n = 5 + 1

= 6

∴ 6^th term of the progression 0.004, 0.02, 0.1, …. is 12.5.