The length of a pencil is 128mm correct to the nearest millimetre - Edexcel - GCSE Maths - Question 3 - 2019 - Paper 2

To find the error interval for a measurement that is given as 128 mm correct to the nearest millimetre, we need to establish the range of values that would round to 128 mm.

Since the measurement is correct to the nearest millimetre, the possible values that could round to 128 mm extend 0.5 mm below and 0.5 mm above 128 mm.

This can be calculated as follows:

• The lower limit is given by:

  $128 - 0.5 = 127.5$

• The upper limit is given by:

  $128 + 0.5 = 128.5$

Thus, the error interval for the length of the pencil can be completed as:

$127.5 \leq \text{length} < 128.5$