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longgone's avatar

Will you help me with this (easy) maths question?

Asked by longgone (6689 points ) December 11th, 2013

I am tutoring my sister. Both of us understand the question, we’ve solved it, and now we’re stuck.

Here it is:
Lanor and Matt are having a race on a 400m track. Lanor runs 220m/minute, Matt 180m. How long until Lanor laps Matt?

Now, obviously, the answer is 10 minutes. Lanor needs to run 400m more than Matt to lap him, and she covers forty extra metres per minute. So, 400/40, which is ten. What I can’t do is express this in an equation, explaining how I got there. Can anyone help?

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4 Answers

ragingloli's avatar

180X+400=220X |-180X
400=40X |:40
10=X

longgone's avatar

Yes. Of course. I, uh…I knew that all along.

Can’t believe it’s that easy. Many thanks!!

LostInParadise's avatar

You can also go with your original idea using relative velocity. Relative velocity is not usually taught in school, but it is completely legitimate and simplifies a lot of problems. Relative to Matt, Lanor runs 220 m/min – 180 m/min =40m/min. You want to know when the relative distance is 400 m. 400m / 40 m/min = 10 minutes.

longgone's avatar

Thanks, @LostInParadise, that could be useful for further explaining.

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