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2.4.12 Calculate probabilities from a Normal distribution (A-level only)

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Question 65

A high-precision industrial sensor measures the deviation of a mechanical component's width from a target value. The deviation, DDD microns, follows a normal distribution with a mean of 82 μm82\ \mu\text{m}82 μm and a standard deviation of 6.0 μm6.0\ \mu\text{m}6.0 μm.

a.

Find the probability that a component selected at random has a deviation greater than 95 μm95\ \mu\text{m}95 μm.

[3]
b.

The machine is recalibrated so that the mean deviation is μ\muμ but the standard deviation remains at 6.0 μm6.0\ \mu\text{m}6.0 μm. Two independent components are measured by the sensor.

The probability that both components have a deviation of less than 75 μm75\ \mu\text{m}75 μm is 0.160.160.16.

Calculate the value of μ\muμ, giving your answer to 1 decimal place.

[4]
c.

A different calibration is tested where the mean deviation is 151515 and the standard deviation is 202020.

The sensor then records 5 independent readings from this distribution.

Determine the probability that the deviation is negative for at least one of these components.

[4]

2.4.12 Calculate probabilities from a Normal distribution (A-level only) Questions

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