Answer:
Part A)
Our system of equation is:
[tex]\displaystyle \begin{aligned} 2x+y&=25\\x+y&=20\end{aligned}[/tex]
Where x represent the amount of cheese wafers bought and y represent the amount of chocolate wafers bought.
Part B)
Mike and his friends bought five cheese wafers and 15 chocolate wafers.
Step-by-step explanation:
Let cheese wafers be represented by x and let chocolate wafers be represented by y.
Part A)
They spent a total of $25. Since each cheese wafer cost $2 and each chocolate wafer cost $1, we can write that:
[tex]2x+1y=25[/tex]
Or, simply:
[tex]2x+y=25[/tex]
They also purchased a total of 20 packets of wafers. Hence:
[tex]x+y=20[/tex]
Our system of equation is:
[tex]\displaystyle \begin{aligned} 2x+y&=25\\x+y&=20\end{aligned}[/tex]
Where x represent the amount of cheese wafers bought and y represent the amount of chocolate wafers bought.
Part B)
Since both equations have the same coefficient for y, we can use elimination. First, multiply the second equation by negative one:
[tex]-x-y=-20[/tex]
Add it to the first equation:
[tex](2x+y)+(-x-y)=(25)+(-20)[/tex]
Simplify:
[tex]x=5[/tex]
So, five cheese wafers were bought.
Using the second equation again, we can see that:
[tex](5)+y=20\Rightarrow y=15[/tex]
So, 15 chocolate wafers were bought.
Notes:
If we wanted to solve this using substitution, we can subtract x (or y, doesn't really matter) from both sides from either equation. Using the second equation, this yields:
[tex]y=20-x[/tex]
Substitute this into the first:
[tex]2x+(20-x)=25[/tex]
Simplify:
[tex]x=5[/tex]
And we will acquire the same answer:
[tex]y=20-(5)=15[/tex]
