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Hi, please could I have some help on this question? I'm confused about the highlighted parts on the markscheme. I got 1239 but all I did was inverse normal of 0.025 with distribution X~N(1300,962).
ms: https://ibb.co/0jJpnfX
Thanks!

I think they have just used the approximation that 95% of the data lies within 2 standard deviations either side of the mean for any normal distribution.
So roughly 2.5% of the data will lie between -infinity and μ - 2σ and roughly 2.5% will lie between μ + 2σ and +infinity.
So it seems this is why the mark scheme uses this strange method - I’d say the inverse normal method is generally best but given how many marks are attached to the question, they’ll want more work for the marks.

thank you, I understand this now but I don't get why they chose 1239 when the P(x<1239) is 0.0251 which is greater than 0.025?

Can’t remember the official reason (if there is one), though I suspect that it’s because 0.0251 is closer to 0.025 than 0.0233 is.