Question

Evaluate S5 for 600 + 300 + 150 + … What's the answer?

Answer 1

Answer:

The answer is 1,162.5 ⇒ answer A

Step-by-step explanation:

The series is 600 + 300 + 150 + ......

∵ 300 ÷ 600 = 0.5

∵ 150 ÷ 300 = 0.5

- Each number multiplied by 0.5 to get the next number, that means

  we have constant ratio in this series between each tow consecutive

  terms then the series is geometric

- The rule of the sum of the geometric series is:

  $S_{n}=\frac{a(1-r^{n})}{1-r}$, where a is the first term in the series,

  r is the constant ratio between each two consecutive terms and n is

  the position of the term in the series

- We need to find $S_{5}$

∵ a = 600 , r = 0.5 and n = 5

Substitute all of these values in the rule above to find $S_{5}$

∴ $S_{5}=\frac{600(1-0.5^{5})}{1-0.5}=1162.5$

The answer is 1,162.5