Math 114N
Week 5 Discussion: Systems of Equations in
the Real World
Initial Post Instructions
If you have a problem that has multiple variables, you can solve it using a system
of equations. Think of a real-world example where you would need to solve using
a system of equations. Write two or three sentences describing your example.
Include the equations in your description, but do not solve the system. That will
be left to your classmates
.
For this week's discussion we are going over system of equations. My example of such
is
My sister and I decided to go to Mcdonalds for dinner. I ordered 3 hot and spicy
sandwiches and 3 medium fry that totaled to $11.25. My sisters total for 4 hot and spicy
sandwiches and 2 medium fry was $10. How much do the hot and spicy sandwiches
and medium fry cost independently.
Our variables will be:
x= cost of a hot and spicy
y= cost of a medium fry
So for my dinner in equation form:
3 hot and spicys and 3 medium fry will cost= $11.25
3x+3y=11.25
My sisters order in equation form:
4 hot and spicys and 2 medium fry=$10
4x+2y=10

Now to find the price of each item I need to rewrite the equation with opposite teams to
find the x value.
So:
2[3x+3y=11.25]
2[3x+3y=11.25]
6x+6y=22.50
6x+6y=22.50
and
−3[4x+2y=10]
−3[4x+2y=10]
−12x−6y=−30
−12x−6y=−30
now we will combine
−12x−6y=−30
−12x−6y=−30
6x+6y=22.50
6x+6y=22.50
−6x=−7.50
−6x=−7.50
−6=−6
−6=−6
x=1.25
x=1.25
Now to find y
4x+2y=10
4x+2y=10
4(1.25)+2y=10
4(1.25)+2y=10
5+2y=10
5+2y=10