For example, look at Q1(a) from the **2018 Probability** paper:

*(a) Over the last seven years, the daily temperatures in Reefton have been found to be approximately normally distributed with a mean of 11.6°C and standard deviation of 4.8°C.*

*Use this approximation to answer the questions in parts (i) to (iv).*

*Working and/or diagrams must be shown. Correct answer(s) alone will generally limit grades to Achievement.*

*(i) Find the probability that a randomly chosen day in Reefton would have a daily *

*temperature between 11.6°C and 18.8°C*

*(ii) Find the probability that a randomly chosen day in Reefton would have a daily temperature over 17°C.*

*(iii) People in Reefton talk about the hottest 1% of days as being “scorchers”.*

*What is the lowest possible daily temperature of a “scorcher” day?*

*(iv) Using this normal distribution approximation, the probability of a daily temperature lower than 9°C is 29.4% (3sf).*

*Suppose that temperatures in Reefton increased due to climate change, but the standard deviation remained the same.*

*What would the mean daily temperature for Reefton need to become to make this probability fall to 20.0% (3sf)*

If you spend a minute briefly looking at the questions, you will notice that (i) and (ii) are one step problems which won’t give you more than a “u” (leading to an Achieved grade). On the other hand, (iii) requires you to calculate Z value and find a value when you know probability. This is a two-step solution and it would usually give you an “r”, which will give you 5 marks (M5) on the question even if you haven’t done the previous two sub-questions. That is because by completing (iii) you would demonstrate the skills required to complete (i) and (ii).

Even a quick look on (iv) tells us that it is a solution in several steps so we would expect an “r” or even “t” for it. Remember, a single “t” mark in one question gives you 7 marks (E7) which is a third of your final Excellence.

So to keep it on the safe side, you could only complete (iii) and (iv), and (iii) would be just in case you made a mistake in (iv) so you would at least get an “r”.

After that you can move on to the next part. If you have completed the Merit/Excellence questions for all 3 questions, and still have time left, you could go back and do the Achieved parts.