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.
[tex]\frac{60}{100} =\frac{21}{x}[/tex]
Now let us solve our equation for x by cross multiplication.
[tex]60\cdot x=21\cdot 100[/tex]
[tex]60\cdot x=2100[/tex]
[tex]x=\frac{2100}{60}=\frac{210}{6}[/tex]
[tex]x=35[/tex]
Therefore, our whole number is 35.
