2 years ago

A Gallon of milk cost $2.79 in 2000.In 2015,It cost $3.98

Mathematics

1 answer:

Naddik [55]2 years ago

4 0

Answer:its 42.65232974910394

Step-by-step explanation:

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Solve the system of equations.<br> <img src="https://tex.z-dn.net/?f=%5Cleft%20%5C%7B%20%7B%7By%3D220x-160%7D%20%5Catop%20%7By%3

Leni [432]

$\begin{cases} y=220x-160\\ y=20x^2-400 \end{cases}\qquad \qquad \stackrel{\textit{substituting on the 2nd equation}}{\stackrel{\textit{\Large y}}{220x-160}~~ = ~~20x^2-400} \\\\\\ -160=20x^2-220x-400\implies 0=20x^2-220x-240 \\\\\\ 0=20(x^2-11x-12)\implies 0=x^2-11x-12 \\\\\\ 0=(x-12)(x+1)\implies x= \begin{cases} 12\\ -1 \end{cases}$

$\dotfill\\\\ x=12\qquad \qquad \stackrel{\textit{substituting on the 1st equation}}{y=220(12)-160}\implies y=2480 \\\\\\ x=-1\qquad \qquad \stackrel{\textit{substituting on the 1st equation}}{y=220(-1)-160}\implies y=-380 \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ ~\hfill (12~~,~~2480)\qquad (-1~~,~~-380)~\hfill$