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## Pre-algebra

### Course: Pre-algebra>Unit 15

Lesson 2: Systems of equations with graphing

# Systems of equations with graphing: chores

Graphical Systems Application Problem. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• why do you need a graph, it whould much easier to do it in your head?
• For this equation, yes it is way easier to do in your head. But much of what you'll do in stats or macroeconomics will be far more complicated. This is a just a simplified version so you learn the concept.
• Anyone else solve this in their head in the first minute? :) I sort of just did it logically, is Sal just trying to show us how to do it a different way?
• I can't figure out how to graph these equations, no matter how many videos I watch about this topic. Can anybody explain?
• To graph these system of equations, you have to graph the unknowns using the y intercept, and the coefficient of x to figure out how the graph grows. You graph the other equation overlapping the first equation on the graph, and the point where the two graphs intersect is the solution.
• Ok, so I think I'm getting it.

The easiest way is doing it with your head - since this is an easy question.

A more complicated way is to graph it...

But is there a way on solving it/finding a solution with just the equation?
• But sometimes in like Algebra 1, you learn parabolas and they are definitely harder to solve in your head and that is when you do the graphing method. But for problems like this I agree with you; algebraically it is much easier.
• At , why is there -B on the right side?
• The negative sign represents -1. So -B is basically -1 * B.
(1 vote)
• What is x + y =z
• you forgot to put the negative 10 its actually 1170
• doing the substitution method I get a=20 and b=30. Why?
• I think you may have mixed something up in your calculation.
A+B=50
A=B+10 Subsituting B+10 for A in the first equation,
(B+10)+B = 50 No subtract 10 from both sides
B+B=40
2B=40 Divide both sides by 2
B=20
Now put 20 in for B in A+B=50, so
A+20=50
A=30

I hope that helps
• I cannot seem to get the equations out of the word problem, any tips on easily finding it? ? ? ?
• What they ask you is unknown. Use letter to represent unknown.
Try to convert words into math expressions. "More by..." or "older by..." or "greater by .." means plus. "Less by.." means minus. "... times older" or "... in each" means multiply.
Hope this helps.
• At , they say abby takes place of the y axis and ben takes places of the x axis, but why can't it be switched around, like instead abby takes of the x axis?