Explain how you can use proportional reasoning to determine the whole if you know that 21 is 60% of the whole

Let the whole number be x.

We have been given that 60% of x is 21. So what proportion is between 60 and 100, the same proportion will be between 21 and x. By using this reasoning we can set these number as proportions.

Now let us solve our equation for x by cross multiplication.  

Therefore, our whole number is 35.

hello from mrbilldoesmath!

answer:

x - 3

discussion:

x^2 - 9 = (x-3) (x+3)   so

(x^2-9)/ (x + 3) = x-3

you,

mrb

30005

yes ok