Question

There are 210 girls in the 7th grade. For every five girls, thereare three boys. Which three (3) proportions can be used to find the numberof boys?The proportions are:1. 5/3 = 210/x2. x/210 = 3/53. x/5 = 3/2104.5/210 = 3/x5. 210/3 = x/5

Answer 1

We know that the ratio for girls and boys is 5:3, this means that there are five girls for three boys. We also know that there are 210 girls but we don't know how many boys there are, nevertheless the ratio should be the same, this means that the proportion we are looking for is:

`(5)/(3)=(210)/(x)`

Then, the first proportion is 1.

If we switch the denominator and numerator in each of the sides of the last equality we get an equivalent one, then:

`(3)/(5)=(x)/(210)`

Then, the second option is 2.

Finally if we pass the five to the right and the x to the left in the last equation we get:

`(3)/(x)=(5)/(210)`

Then, the thir option is 4.