2020 · Q34
In a class room the ratio of number of girls to that of boys is 3 : 4. The average height of students in the class is 4.6 feet. If the average height of the boys in the class is 4.8 feet, then what is the average height of the girls in the class?
Elementary MathematicsStatistics
- ALess than 4.2 feet
- BMore than 4.2 feet but less than 4.3 feet
- CMore than 4.3 feet but less than 4.4 feet
- DMore than 4.4 feet but less than 4.5 feet
Explanation
With girls : boys = 3 : 4, the overall mean is (3g + 4 × 4.8)/7 = 4.6, where g is the girls' mean. Then 3g = 32.2 − 19.2 = 13, so g = 13/3 ≈ 4.33 — more than 4.3 but less than 4.4. Indeed 13/3 ≈ 4.333, which lies strictly between 4.3 and 4.4.