The distance in kilometres () of an observer from the centre of a thunderstorm can be estimated by counting the number of seconds () between seeing the lightning and first hearing the thunder.

Use the formula    to estimate the number of seconds between seeing the lightning and hearing the thunder if the storm is 2.1 km away.   (1 mark)

For adults (18 years and older), the Body Mass Index is given by:
  

,    where   mass in kilograms and   height in metres.
  

The medically accepted healthy range for    is  .

What is the minimum weight for a 172 cm adult female to be considered healthy, correct to 1 decimal place? (2 marks)

The distance, metres, travelled by a car slowing down from km/h to km/h can be obtained using the formula

What distance does a car travel while slowing down from 100 km/h to 70 km/h?   (2 marks)