0 and 0decay factor. The decay factor can be also written as 1-r, where r is the percent rate of change expressed as a decimal. Therefore, we can write the exponential decay function as'>

Pearson Algebra 1 Common Core, 2011
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Exercise 20 Page 479

Practice makes perfect
a Let's recall the exponential decay function.
y=a* b^x Here, a>0 and 0decay factor. The decay factor can be also written as 1-r, where r is the percent rate of change expressed as a decimal. Therefore, we can write the exponential decay function as shown below.

y=a* (1-r)^x Finally, let's take a look at the given function, which models the car's value after x years. y=30 000(0.85)^x We can see that the decay factor is equal to 0.85. As we have mentioned before, it can be rewritten in the form 1-r. 0.85=1-0.15 Therefore, the car's value depreciates by 15 % each year.

b Let's take a look at the given function.
y=30 000(0.85)^x Here y describes the car's value after x years. To find out what the value of the car will be in 1 year we have to substitute 1 for x. Let's do it!
y=30 000(0.85)^x
y=30 000(0.85)^1
Simplify
y=30 000(0.85)
y=25 500
After one year the car will be worth about $25 500.
c Let's take a look at the given function.
y=30 000(0.85)^x Here y describes the car's value after x years. To find out what the value of the car will be in 4 years we have to substitute 4 for x. Let's do it!
y=30 000(0.85)^x
y=30 000(0.85)^4
Simplify
y=15 660.1875
y≈ 15 660.19
After four years the car will be worth about $15 660.19.