Question

Evaluate S5 for 400 + 200 + 100 + … and select the correct answer below.
25
775
1,125
500

Answer 1

the series is geometric
that is term/previous term equals 1/2
200/400=100/200=1/2

so 400 divided by 2 is 200
200 divided by 2 is 100
100 divided by 2 is 50
50 divided by 2 is 25

so you have your 5 terms...
400+200+100+50+25

Answer 2

you can also use the following formula:
\[S_n=a \cdot \frac{1-r^n}{1-r} \\ \text{ where } n \text{ is the number of the terms } \\ a \text{ is the first number in the sequence } \\ r \text{ is the common ratio }\]

Answer 3

thank you!

Answer 4

np