**1.** What is the sum of the first 7 terms of the series −4+8−16+32−...?

**2.** What is the sum of the series?

4+12+36+108+...+8748

**3.** A car dealership sold one car in its first month of business. The number of cars it sold doubled each month. What was the total number of cars the dealership sold during the first 12 months?

**4.** Michaela drops a ball vertically from a height of 80 feet. The peak height after each bounce is half the previous height.

How far does the ball travel from the time she drops it until it reaches the peak height after the 5th bounce?

jbouyer Mar 1, 2018

#1**+2 **

1. -4 + 8 - 16 + 32 - 64 + 128 - 256 =

(-4 + 8) + (-16 + 32) + (-64 + 128) - 256 =

4 + 16 + 64 - 256 =

84 - 256 =

-172

Second one

4 + 12 + 36 + 108 + .....+ 8748

We need to find what term the last is

We can solve this

4*3^(n-1) = 8748 divide both sides by 4

3^(n - 1) = 2187 take the log of both sides

log 3^(n- 1) = log 2187 and we can write

(n - 1) log 3 = log 2187 divide both sides by log 3

(n - 1) = log 2187 / log 3

n - 1 = 7 add 1 to both sides

n = 8

The sum is given by

4 ( 1 - 3^8) / ( 1 - 3) = 13,120

CPhill Mar 1, 2018

#2**+2 **

Third one

We have

1 + 2 + 4 + .....+ 2^(n - 1)

The sum is

1 ( 1 - 2^12) / ( 1 - 2) = 4095 cars

Last one

The total distance traveled in the first 5 bounces is

80 + 80 ( 1 - (1/2)^(5 - 1) ) / ( 1 - 1/2) = 230 ft

And the distance traveled from the 5th bounce to the next peak is 80 (1/2)^5 = 2.5 ft

So...the total distance traveled is 230 + 2.5 = 232.5 ft

CPhill Mar 1, 2018