Standard the random variable [tex]X[/tex] using the transformation
[tex]Z=\dfrac{X-\mu}\sigma[/tex]
where [tex]\mu[/tex] and [tex]\sigma[/tex] are the mean and standard deviation of [tex]X[/tex], respectively.
[tex]\mathbb P(X\ge170)=\mathbb P\left(\dfrac{X-110}{30}\ge\dfrac{170-110}{30}\right)=\mathbb P(Z\ge2)[/tex]
Now, you can recall that for any normal distribution, approximately 95% of its data falls within 2 standard deviations of the mean, so to either side, there is approximately 2.5% of data that falls below 2 standard deviations from the mean, and 2.5% that falls [tex]2\sigma[/tex] above [tex]\mu[/tex]. In other words, [tex]\mathbb P(Z\ge2)\approx0.025[/tex].
