Answer:
(b) is true
Step-by-step explanation:
Given
Molly
--- starting balance
--- monthly rate
Her brother
---- starting balance
--- annual rate
Required
Determine which option is true
First, we calculate her brother's function.
The function is an exponential function calculated as:
![y = ab^x](https://tex.z-dn.net/?f=y%20%3D%20ab%5Ex)
Where ![b = 1 + r](https://tex.z-dn.net/?f=b%20%3D%201%20%2B%20r)
So, we have:
![y = ab^x](https://tex.z-dn.net/?f=y%20%3D%20ab%5Ex)
![y = 100 *(1 + 10\%) ^x](https://tex.z-dn.net/?f=y%20%3D%20100%20%2A%281%20%2B%2010%5C%25%29%20%5Ex)
![y = 100 *(1 + 0.10) ^x](https://tex.z-dn.net/?f=y%20%3D%20100%20%2A%281%20%2B%200.10%29%20%5Ex)
![y = 100 *(1.10) ^x](https://tex.z-dn.net/?f=y%20%3D%20100%20%2A%281.10%29%20%5Ex)
Hence:
![g(x) = 100 *(1.10) ^x](https://tex.z-dn.net/?f=g%28x%29%20%3D%20100%20%2A%281.10%29%20%5Ex)
Next, we calculate Molly's function (a linear function)
The monthly function is:
![y = mx + a](https://tex.z-dn.net/?f=y%20%3D%20mx%20%2B%20a)
So, we have:
![y = 10x + 500](https://tex.z-dn.net/?f=y%20%3D%2010x%20%2B%20500)
Annually, the function will be:
![y = 10x*12 + 500](https://tex.z-dn.net/?f=y%20%3D%2010x%2A12%20%2B%20500)
![y = 120x + 500](https://tex.z-dn.net/?f=y%20%3D%20120x%20%2B%20500)
So, we have:
![f(x) = 120x + 500](https://tex.z-dn.net/?f=f%28x%29%20%3D%20120x%20%2B%20500)
At this point, we have:
---- Molly
---- Her brother
<u>Next, we test each option</u>
(a): Molly's account will have a faster rate of change over [32,40]
We calculated Molly's function to be:
![y = 120x + 500](https://tex.z-dn.net/?f=y%20%3D%20120x%20%2B%20500)
The slope of a linear function with the form:
is m
By comparison:
![m = 120](https://tex.z-dn.net/?f=m%20%3D%20120)
Since Molly's account is a linear function, the rate of change over any interval will always be the same; i.e.
![m = 120](https://tex.z-dn.net/?f=m%20%3D%20120)
For his brother:
Rate of change is calculated using:
![m = \frac{g(b) - g(a)}{b - a}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7Bg%28b%29%20-%20g%28a%29%7D%7Bb%20-%20a%7D)
![m = \frac{g(40) - g(32)}{40 - 32}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7Bg%2840%29%20-%20g%2832%29%7D%7B40%20-%2032%7D)
![m = \frac{g(40) - g(32)}{8}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7Bg%2840%29%20-%20g%2832%29%7D%7B8%7D)
Calculate g(40) and g(32)
![g(x) = 100 *(1.10) ^x](https://tex.z-dn.net/?f=g%28x%29%20%3D%20100%20%2A%281.10%29%20%5Ex)
![g(40) = 100 * 1.10^{40} =4526](https://tex.z-dn.net/?f=g%2840%29%20%3D%20100%20%2A%201.10%5E%7B40%7D%20%3D4526)
![g(32) = 100 * 1.10^{32} = 2111](https://tex.z-dn.net/?f=g%2832%29%20%3D%20100%20%2A%201.10%5E%7B32%7D%20%3D%202111)
So, we have:
![m = \frac{4526 - 2111}{8}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7B4526%20-%202111%7D%7B8%7D)
![m = \frac{2415}{8}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7B2415%7D%7B8%7D)
![m = 302](https://tex.z-dn.net/?f=m%20%3D%20302)
By comparison: ![302 > 120](https://tex.z-dn.net/?f=302%20%3E%20120)
Hence, her brother's account has a faster rate over [32,40]
(a) is false
(b): Molly's account will have a slower rate of change over [24,30]
--- Molly's rate of change
For his brother:
![m = \frac{g(b) - g(a)}{b - a}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7Bg%28b%29%20-%20g%28a%29%7D%7Bb%20-%20a%7D)
![m = \frac{g(30) - g(24)}{30 - 24}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7Bg%2830%29%20-%20g%2824%29%7D%7B30%20-%2024%7D)
![m = \frac{g(30) - g(24)}{6}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7Bg%2830%29%20-%20g%2824%29%7D%7B6%7D)
Calculate g(30) and g(24)
![g(x) = 100 *(1.10) ^x](https://tex.z-dn.net/?f=g%28x%29%20%3D%20100%20%2A%281.10%29%20%5Ex)
![g(40) = 100 * 1.10^{30} =1745](https://tex.z-dn.net/?f=g%2840%29%20%3D%20100%20%2A%201.10%5E%7B30%7D%20%3D1745)
![g(32) = 100 * 1.10^{24} = 985](https://tex.z-dn.net/?f=g%2832%29%20%3D%20100%20%2A%201.10%5E%7B24%7D%20%3D%20985)
So, we have:
![m = \frac{g(30) - g(24)}{6}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7Bg%2830%29%20-%20g%2824%29%7D%7B6%7D)
![m = \frac{1745 - 985}{6}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7B1745%20-%20985%7D%7B6%7D)
![m = \frac{760}{6}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7B760%7D%7B6%7D)
![m = 127](https://tex.z-dn.net/?f=m%20%3D%20127)
By comparison: ![127 > 120](https://tex.z-dn.net/?f=127%20%3E%20120)
Hence, Molly's account has a slower rate over [24,30]
(b) is false
(c): Molly's account will have a slower rate of change over [0,4]
--- Molly's rate of change
For his brother:
![m = \frac{g(b) - g(a)}{b - a}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7Bg%28b%29%20-%20g%28a%29%7D%7Bb%20-%20a%7D)
![m = \frac{g(4) - g(0)}{4 - 0}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7Bg%284%29%20-%20g%280%29%7D%7B4%20-%200%7D)
![m = \frac{g(4) - g(0)}{4}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7Bg%284%29%20-%20g%280%29%7D%7B4%7D)
Calculate g(4) and g(0)
![g(x) = 100 *(1.10) ^x](https://tex.z-dn.net/?f=g%28x%29%20%3D%20100%20%2A%281.10%29%20%5Ex)
![g(4) = 100 * 1.10^4 =146](https://tex.z-dn.net/?f=g%284%29%20%3D%20100%20%2A%201.10%5E4%20%3D146)
![g(0) = 100 * 1.10^{0} = 100](https://tex.z-dn.net/?f=g%280%29%20%3D%20100%20%2A%201.10%5E%7B0%7D%20%3D%20100)
So, we have:
![m = \frac{g(4) - g(0)}{4}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7Bg%284%29%20-%20g%280%29%7D%7B4%7D)
![m = \frac{146 - 100}{4}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7B146%20-%20100%7D%7B4%7D)
![m = \frac{46}{4}](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7B46%7D%7B4%7D)
![m = 11.5](https://tex.z-dn.net/?f=m%20%3D%2011.5)
By comparison: ![120>11.5](https://tex.z-dn.net/?f=120%3E11.5)
Hence, Molly's account has a faster rate over [0,4]
(c) is false