sws._.
Christopher is 4 times as old as Michael. Ten years ago, Christopher was 9 times as old as Michael.How old is Christopher now?
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geoffb
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Are you able to turn the sentence into an equation?
sws._.
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yeah
sws._.
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i think that is what im supposed to do, but im having trouble setting it up
geoffb
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Okay, no problem. Do you have a guess as to how you would start?
sws._.
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4x-10 is this one side of the equation?
geoffb
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Can you write an equation for right now? Let's say time = 0 right now.
sws._.
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yeah
geoffb
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Use C and M for your variables.
sws._.
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okay but how would i set it up?
geoffb
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"Christopher is 4 times as old as Michael." Write that algebraically.
sws._.
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4m ?
geoffb
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What is 4M?
sws._.
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4 times michaels age
sws._.
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4 * M
geoffb
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Right. But you need an equals sign and something on the other side. For example, if steak is 10 times heavier than rice, steak = 10 * rice, which as a formula would be S = 10R
geoffb
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So how would you write a formula for "Christopher is 4 times as old as Michael?"
sws._.
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4m=10(4x-9) ? i have no idea ._.
geoffb
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That's okay. Not to worry. It's C = 4M
geoffb
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Does that make sense?
geoffb
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That is a perfectly valid statement for right now. Now, the tougher part, you need to write a formula for 10 years ago.
sws._.
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oh okay i know that 10 has to be outside the parenthesis
sws._.
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no wait..
sws._.
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does 9 go outside?
sws._.
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because it says 9 times as old as Christopher
geoffb
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On the side where parentheses matter, the 10 will actually need to go inside.
You need to write an equation for the second statement which uses the variables for their current ages. That might sound complex, but it's as simple as:
My current age might be x.
I can say that 10 years ago, my age was x - 10. It doesn't matter what x represents; x - 10 is valid no matter what.
sws._.
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ohhh
geoffb
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Yes, right! The 9 goes outside.
sws._.
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okay so it would be 9(x-10) ?
geoffb
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Yes! But what is x?
sws._.
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i mean c. im using x instead of c
geoffb
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Remember, you need an equal sign, and stuff on both sides of it.
geoffb
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Okay, we can use x instead of C. But then what are we using instead of M?
geoffb
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Remember, for now, we are keeping their ages separate.
sws._.
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i guess we can use y or m but i like x instead of c
geoffb
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Sure. Okay, so in the formula I gave before, x = 4y
Chris (x) is 4 times older than Michael (y) right now.
geoffb
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So now, we need to do our "10 years ago" formula.
sws._.
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would it be the one i mentioned before?
geoffb
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Yes, but you used x. It should be y.
geoffb
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And you need your full formula.
geoffb
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But you're doing great.
geoffb
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@sws._. Mention me if you feel like continuing. I'd like to help you learn this so you can do your other 11 questions.