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# Linear function example: spending money

Sal solves an interesting application problem using a linear model. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• When Sal makes the graph, doesn't the x and y-axis have to have the same increments?
• they don't have to have the same increments but it's just ussually that they do
• but taking the graph takes much time than substituting the value of "x" in the equation.so,what is the use of solving with graph?
• Sal started to hint at the importance of graphs with this word problem by assigning different types of values to each axis (money and days). Graphs, or charts, are used a lot in research and business to help visualize data. As you move into other math topics, including geometry and trig, you will start to see more practical uses for graphing, but you have to start somewhere to gain the fundamentals those other topics and uses rely on.
• Why did he make a whole line of answers when the question clearly states that x=8?
• Well, I guess he wanted to show us how to do this.
Also for a clear graph
• why can't she be in the hole?()
• In this case He is saying that she won't go into debt, the graph goes into
the negative Y quardinate but for this example we are just not looking at those values.
• Khan academy for big brains and small brains
• What if the x in the table is money and the y in the table is the days? I figured out that it is harder to do the equation plugging in the numbers( Y=40 - 2.5x while Y=8 ). Is there anyway I can know which way is easier like sal always does? Does he do the equation in his head before he gives his explanation to find which one is easier?
• Generally speaking, x is our independent variable and y is our dependent variable. That is, y is the variable that is determined by the other variable. If you did y=40-2.5x when y=8, you are solving a different problem. You are finding out how many days pass before she has \$8 left.
• why are almost all these comments irrelevant to the video-
• helloooo:) have a great day even though you have to do life
• Where does the 2.5 come from? No where in the original question does it tell us how much she is spending at a time. Explain the 2.5 data, please.
Dana Goodale