Answer:
137
Explanation:
Use the formula for exponential growth:
f(x) = a(1 + r)^x
In this formula, f(x) is the resulting number, in this case the number of fast food stores. a is the initial value, in this case 50. r is the growth rate, which they told you was 7%. And x is the number of time intervals, which is how many years between 1990 and 2005.
Substitute the known values into the equation:
f(x) = a(1 + r)^x
r is going to be 0.07 because the growth rate in the equation is the decimal form of 7%. x will be 15 because 2005-1990 = 15
f(x) = 50(1 + 0.07)^15
f(x) = 50(1.07)^15
Now just solve.
f(x) = 50(1.07)^15
First raise 1.07 to the 15th power.
f(x) = 50(2.75903154)
Then simplify.
f(x) = 137.951577
They want the approximate amount, so round it down to 137. The number actually rounds to 138, but he doesn't have a full 138 stores, so you use 137.