Kelly and Eddie are each saving money for a motorcycle. The total amount of money, in dollars, that Kelly will save over x weeks is modeled by the function f(x)=60+50x. The total amount of money, in dollars, that Eddie will save over x weeks is modeled by the function g(x)=2

x
.
Graph the functions in the same coordinate plane to determine when f(x)=g(x). After how many weeks, rounded to the nearest integer, will they have saved the same amount of money?
A. 9 weeks
B. 510 weeks
C. 60 weeks
D. 1 week

1 answer

To find when \( f(x) = g(x) \), we need to set the two functions equal to each other:

\[ f(x) = 60 + 50x \] \[ g(x) = 2^x \]

Setting them equal gives us:

\[ 60 + 50x = 2^x \]

To find the solution, let's solve this equation graphically. First, we will graph both functions separately and find where they intersect.

  1. Graphing \( f(x) = 60 + 50x \): This is a linear function with a y-intercept of 60 and a slope of 50. It will increase continuously as \( x \) increases.

  2. Graphing \( g(x) = 2^x \): This is an exponential function that starts at (0, 1) and increases rapidly for positive values of \( x \).

To find where these two functions intersect, we can evaluate both functions for various integer values of \( x \):

  • For \( x = 0 \):
    \( f(0) = 60 + 50 \cdot 0 = 60 \)
    \( g(0) = 2^0 = 1 \)

  • For \( x = 1 \):
    \( f(1) = 60 + 50 \cdot 1 = 110 \)
    \( g(1) = 2^1 = 2 \)

  • For \( x = 2 \):
    \( f(2) = 60 + 50 \cdot 2 = 160 \)
    \( g(2) = 2^2 = 4 \)

  • For \( x = 3 \):
    \( f(3) = 60 + 50 \cdot 3 = 210 \)
    \( g(3) = 2^3 = 8 \)

  • For \( x = 4 \):
    \( f(4) = 60 + 50 \cdot 4 = 260 \)
    \( g(4) = 2^4 = 16 \)

  • For \( x = 5 \):
    \( f(5) = 60 + 50 \cdot 5 = 310 \)
    \( g(5) = 2^5 = 32 \)

  • For \( x = 6 \):
    \( f(6) = 60 + 50 \cdot 6 = 360 \)
    \( g(6) = 2^6 = 64 \)

  • For \( x = 7 \):
    \( f(7) = 60 + 50 \cdot 7 = 410 \)
    \( g(7) = 2^7 = 128 \)

  • For \( x = 8 \):
    \( f(8) = 60 + 50 \cdot 8 = 460 \)
    \( g(8) = 2^8 = 256 \)

  • For \( x = 9 \):
    \( f(9) = 60 + 50 \cdot 9 = 510 \)
    \( g(9) = 2^9 = 512 \)

  • For \( x = 10 \):
    \( f(10) = 60 + 50 \cdot 10 = 560 \)
    \( g(10) = 2^{10} = 1024 \)

From our calculations, we can see:

  • At \( x = 9 \), \( f(9) = 510 \) and \( g(9) = 512 \).
  • At \( x = 8 \), \( f(8) = 460 \) and \( g(8) = 256 \).

Therefore, the two values are very close at \( x = 9 \).

Thus, the answer is: A. 9 weeks.