Originally Posted by

**looi76** **Question**

The time taken by a garage to replace worn-out brake pads follows a normal distribution with mean 90 minutes and standard deviation 5.8 minutes. The garage claims to complete the replacement in '*a* to *b* minutes'. If this claim is to be correct for 90% of the repairs, find *a* and *b* correct to 2 significant figures, based on a symmetrical intervals centred on the mean.

**Attempt:**

I only know that $\displaystyle \mu = 90$ and $\displaystyle \sigma = 5.8$. I can't understand what the question exactly means. How am I suppose to find the values of *a* and *b* ?