If there are 7:5 boys and girls in a class and there are 21 girls how many boy are there in the class?
Cross multiply and solve for x.
7/5 = x/21
21girls to 15boys
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21 girls to 13 boys
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21 girls to 13 boys
To find out how many boys are there in the class, we need to use the information that there is a ratio of 7:5 boys to girls.
First, we need to calculate the total number of parts in the ratio. This is done by adding the numbers in the ratio together: 7 + 5 = 12.
Next, we divide the total number of girls in the class (21) by the number of parts representing girls in the ratio (5) to find the value of one part of the ratio: 21 / 5 = 4.2.
Since we can’t have a fraction of a person, we must round this value to the nearest whole number. In this case, 4 is the nearest whole number.
Finally, we can multiply the value of one part (4) by the number of parts representing boys in the ratio (7) to find the total number of boys in the class: 4 * 7 = 28.
Therefore, there are 28 boys in the class.