Question : Out of 20 boys, 6 are 1 m 15 cm in height, 8 are 1 m 10 cm and the rest are 1 m 12 cm. The average height of all of them is:
Option 1: 112.1 cm
Option 2: 121.1 cm
Option 3: 121 cm
Option 4: 112 cm
Correct Answer: 112.1 cm
Solution :
Convert the heights into centimetres (cm)
6 boys of 1 m 15 cm i.e. 115 cm
8 boys of 1 m 10 cm i.e. 110 cm
The remaining 20 – (6 + 8) = 6 boys are of 1 m 12 cm i.e. 112 cm
Now average=
$\frac{(6 × 115) + (8 × 110) + (6×112)}{20}$
= $\frac{(690 + 880 + 672)}{20}$
= $\frac{2242}{20}$
= 112.1 cm
Hence, the correct answer is 112.1 cm.
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