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## sws._. 3 years ago 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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1. geoffb

Are you able to turn the sentence into an equation?

2. sws._.

yeah

3. sws._.

i think that is what im supposed to do, but im having trouble setting it up

4. geoffb

Okay, no problem. Do you have a guess as to how you would start?

5. sws._.

4x-10 is this one side of the equation?

6. geoffb

Can you write an equation for right now? Let's say time = 0 right now.

7. sws._.

yeah

8. geoffb

Use C and M for your variables.

9. sws._.

okay but how would i set it up?

10. geoffb

"Christopher is 4 times as old as Michael." Write that algebraically.

11. sws._.

4m ?

12. geoffb

What is 4M?

13. sws._.

4 times michaels age

14. sws._.

4 * M

15. geoffb

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

16. geoffb

So how would you write a formula for "Christopher is 4 times as old as Michael?"

17. sws._.

4m=10(4x-9) ? i have no idea ._.

18. geoffb

That's okay. Not to worry. It's C = 4M

19. geoffb

Does that make sense?

20. geoffb

That is a perfectly valid statement for right now. Now, the tougher part, you need to write a formula for 10 years ago.

21. sws._.

oh okay i know that 10 has to be outside the parenthesis

22. sws._.

no wait..

23. sws._.

does 9 go outside?

24. sws._.

because it says 9 times as old as Christopher

25. geoffb

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.

26. sws._.

ohhh

27. geoffb

Yes, right! The 9 goes outside.

28. sws._.

okay so it would be 9(x-10) ?

29. geoffb

Yes! But what is x?

30. sws._.

i mean c. im using x instead of c

31. geoffb

Remember, you need an equal sign, and stuff on both sides of it.

32. geoffb

Okay, we can use x instead of C. But then what are we using instead of M?

33. geoffb

Remember, for now, we are keeping their ages separate.

34. sws._.

i guess we can use y or m but i like x instead of c

35. geoffb

Sure. Okay, so in the formula I gave before, x = 4y Chris (x) is 4 times older than Michael (y) right now.

36. geoffb

So now, we need to do our "10 years ago" formula.

37. sws._.

would it be the one i mentioned before?

38. geoffb

Yes, but you used x. It should be y.

39. geoffb

And you need your full formula.

40. geoffb

But you're doing great.

41. geoffb

@sws._. Mention me if you feel like continuing. I'd like to help you learn this so you can do your other 11 questions.

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