Question 25721
24Boys and 16Girls


Find total of Boy and Girls in class.
15% = 6,         15/100 = 6/X,       X x 15/100 = 6/X x X,      which is 15X/100 = 6

100 x 15X/100 = 6 x 100, which is15X = 600,         

1/15 x 15X = 600 x 1/15, which is X = 40
(Number of Boys and Girls in class is 40)

Find numerical value for 60% of 40
60/100 = X/40,       40 x 60/100 = X/40 x 40,  which is 2400/100 = X

X = 2400/100   IS    X = 24.   24 Boys – 40 = 16 Girls

24 Boys and 16 Girls

Explation:

If 6 girls were taken away and the percentage of boys when from 60% to 75%, then 6 students equal 15%. Now, from here there are a few ways to do this… unfortunately I always seem to find the most difficult way possible to solve things… sorry. So, if 15 % (15/100), is (=) 6, then 100% of number of students must be… X (unknown), now to solve for X.			15 over 100 equal 6 over X.   

15/100=6/X, so X is currently a denominator (1/X), it must first be a numerator (X/1 or X … it’s the same thing). Cross-multiply by multiplying Both Sides of the equation by X/1. This will cause the left side to have 15X/100 and the right side to have 6X/X (which can now be looked at as just 6x1 = 6.   

15X/100 = 6, is the current stage of our problem. We must get X ALONE on one side, so next move the 1/100 part of 15X/100 to the right side by multiplying Both Sides by 100. So 15X/100 x 100 (or 100/1) because 100/100 is 1 this side can now be read as 15X x 1 = 15X. The right side is 6 x 100 = 600.

15X = 600, is the current stage. Because 15X can also be read as 15 x X, we can divide Both Sides by 15 ( the same as multiplying by 1/15). So the left side is 15X/15, which is like 15/15 x X, WHICH is like 1 x X which is just X. The right side is 600/15 = 40. So  X = 40  …….good…but, we still didn’t answer the original question. 

So, X (100% of the number of students) is 40. The question told us that 60% of the students were boys, so 60/100 = X/40 (X being the numerical value of 60%), Multiply Both Side by 100 and then 40, which should end up as 100X= 2400, divied Both Side by 100, so now X =24…. 24 boys and the rest of the 40 must be 16 girls.

24Boys and 16Girls