WAEC - Further Mathematics (2010 - No. 20)
The mean age of 15 pupils in a class is 14.2 years. One new pupil joined the class and the mean changed to 14.1 years. Calculate the age of the new pupil.
12.4 years
12.6 years
13.2 years
14.1 years
Wyjaśnienie
\(Mean = \frac{\text{sum of ages}}{\text{no of pupils}}\)
Let the sum of the ages of the 15 pupils be x and the sum of the 16 pupils be y.
\(\frac{x}{15} = 14.2 \implies x = 14.2 \times 15 = 213\)
\(\frac{y}{16} = 14.1 \implies y = 14.1 \times 16 = 225.6\)
\(\text{Age of new pupil} = 225.6 - 213 = 12.6\)