# Quick Question - Math SL

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I was wondering if you guys could help me out in a quick Math SL question:

The speeds of lorries through a village are normally distributed with a mean of 65 km h-1 and a standard deviation of 12 km h-1. Given that 10.56% of lorries are breaking the speed limit, what is the speed limit?

Thank you!

Edited by ibboy11

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I apologize if this is complete rubbish in the end.

Okay, so your

s.d=12

mean=65

and we are looking for 10.56% over the the number we are looking for. That number we will call X

So we would have a formula that would look like this:

1- P(Z<(X-m/sd))=(not sure what variable this would be? P?)

You would have to standardize it to get the Z, you probabaly know. Then plug it in like this and you should be able to get the answer. If not, blah, probabaly my fault for making up math. Hopefully someone will come and fix it.

1-P(Z<(X-65/12))=10.56

Then to solve for X you would do the invNorm of 10.56. and set that equal to (X-65/12) I believe. I am so sorry if I didn't tell you how to do this right. Gah.

Edited by Dark Matter

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