SAJC Normal Distribution Tutorial Set 2

The masses of bars of chocolate are normally distributed with mean \(\mu \) kg and standard deviation \(\sigma \) kg. It is known that \(20\%\) of the bars of chocolate have masses which differ from \(\mu \) kg by at most \(m\) kg. Find the probability that a randomly chosen bar of chocolate has a mass which exceeds \(\mu \) kg by at least \(3m\) kg.