A model railway is built using the scale 1 : 87 - OCR - GCSE Maths - Question 13 - 2017 - Paper 1

To find the distance between the rails for the full-size train, we first convert the model distance into meters. Given the scale is 1:87, we can use the following formula:

$$ext{Real Distance} = ext{Model Distance} \times ext{Scale Factor}$$

Here, the model distance is 16.5 mm, which must be converted to meters:

$$ext{Model Distance in meters} = 16.5 ext{ mm} \times \frac{1 ext{ m}}{1000 ext{ mm}} = 0.0165 ext{ m}$$

Now applying the scale factor:

$$ext{Real Distance} = 0.0165 ext{ m} \times 87 = 1.4355 ext{ m}$$

Thus, the distance between the rails for a full-size train is approximately 1.44 m when rounded to three significant figures.