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2.3.2 Conditional probability (A-level only)

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Question 78

The volume, VVV ml, of a high-precision chemical reagent in automated filling bottles is normally distributed such that V∼N(500,82)V \sim N(500, 8^2)V∼N(500,82).

a.

Find the probability that a randomly selected bottle contains more than 512512512 ml.

[2]
b.

Determine (i) the upper quartile (Q3Q_3Q3​) of VVV (ii) the lower quartile (Q1Q_1Q1​) of VVV

[2]
c.

A bottle is defined as an outlier if its volume is greater than Q3+1.5×(Q3−Q1)Q_3 + 1.5 \times (Q_3 - Q_1)Q3​+1.5×(Q3​−Q1​) or less than Q1−1.5×(Q3−Q1)Q_1 - 1.5 \times (Q_3 - Q_1)Q1​−1.5×(Q3​−Q1​).

Calculate the upper and lower volume limits for outliers.

[2]
d.

A bottle is selected at random.

Using standardisation, show that the probability that this bottle is not an outlier is 0.9930.9930.993 to 3 decimal places.

[3]
e.

Given that this bottle is not an outlier,

showing your working, find the probability that the volume of reagent in this bottle is less than 488488488 ml.

[4]

2.3.2 Conditional probability (A-level only) Questions

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