Common Mistakes (Math)

Qn: Some street lights were positioned at equal intervals apart. If the first and the 10th street lights were 18 metres apart, how far apart were the 3rd and the 18th street light?

Observation: Students often have the misconception that there are 10 intervals between the first and 10th street light. Therefore, the common mistake made:

(18/10) x (18 - 3) = 27m.

The correct solution should be

(18/9) x (18-3)=30m. This is because there are only 9 intervals between the 1st and 10th street lights. Hence, the distance should be 30m.