Answer: Option (a)
Explanation:
To find out which of the given ratios cannot be the ratio of the number of boys and girls in the class, we need to determine whether each ratio produces a whole number when multiplied by the class strength (70).
a. 9:2 means there are 9+2=11 parts in the ratio.
The number of boys = 9/11 x 70 = 630/11
The number of girls = 2/11 x 70 = 140/11
Both the numbers are not whole numbers, therefore, 9:2 cannot be the ratio of boys and girls in the class.
b. 11:3 means there are 11+3=14 parts in the ratio.
The number of boys = 11/14 x 70 = 55
The number of girls = 3/14 x 70 = 15
Both the numbers are whole numbers, therefore, 11:3 could be the ratio of boys and girls in the class.
c. 2:5 means there are 2+5=7 parts in the ratio.
The number of boys = 2/7 x 70 = 20
The number of girls = 5/7 x 70 = 50
Both the numbers are whole numbers, therefore, 2:5 could be the ratio of boys and girls in the class.
d. 3:2 means there are 3+2=5 parts in the ratio.
The number of boys = 3/5 x 70 = 42
The number of girls = 2/5 x 70 = 28
Both the numbers are whole numbers, therefore, 3:2 could be the ratio of boys and girls in the class.
Therefore, the ratio that cannot be the ratio of the number of boys and girls in the class is 9:2. So, the correct answer is option (a).