IB Maths AA HL Sl 4 12 Standardizing Normal Variables Topic Practice

EITHER
$k=1.96 \frac{\sigma}{\sqrt{n}}$ or $1.96 \operatorname{std}(\bar{X})$
k=0.877 or $1.96 \sqrt{0.2}$

OR
The expression is equivalent to
$P\left(320-40 k \leq \sum X \leq 320+40 k\right)=0.95$
k=0.875

Note: Accept any answer that rounds to 0.87 or 0.88 .
Award M1A0 if modulus sign ignored and answer obtained rounds to 0.74 or 0.75
Total