in a school 1620 pupils the ratio of boys to girls is 4:5. what is the nunber of girls in the school??????????

Guest Oct 18, 2014

#3**+5 **

I quite like to do these without algebra - I'll see if I can demonstrate my method.

the black numbers are the ones you have been given.

the ratio of boys to girls is 4:5 so in total there is some multiple of 9 students altogether.

Next you have to say

$$\begin{tabular}{|c|c|c|}\hline

boys & girls & Total\\\hline

4&5&\textcolor[rgb]{1,0,0}{4+5=9} \\\hline

& &1620\\\hline

\end{tabular}$$

$$\\\textcolor[rgb]{1,0,0}{1620\div 9 = 180} \quad $180 is the multiplication factor$\\

so\\

$number of boys is $4\times 180 = 720 \quad $Put that in the box under the 4$\\

and\\

$number of girls is $5\times 180 = 900 \quad $Put that in the box under the 5$\\\\

$Total number of $ \textcolor[rgb]{0,0,1}{ \;purple\;penguins\;} $ is $ 720+900=1620 $ that checks out very nicely. $

\\\\

$The purple penguins is an insider joke - don't worry if you don't get it - you can google it if you want, then you will know what I am talking about. $$$

Melody
Oct 19, 2014

#1**0 **

If the ratio of boys to girls is 4:5, then the ratio of girls to boys is 1:5, which is 1/5.

1/5 of 1620 = (1/5) x 1620 = 324

geno3141
Oct 18, 2014

#2**+5 **

If the ratio is 4:5, then 4/9 are boys and 5/9 are girls.

Then....5/9 x 1620 = 900 girls

And 4/9 x 1620 = 720 boys

CPhill
Oct 18, 2014

#3**+5 **

Best Answer

I quite like to do these without algebra - I'll see if I can demonstrate my method.

the black numbers are the ones you have been given.

the ratio of boys to girls is 4:5 so in total there is some multiple of 9 students altogether.

Next you have to say

$$\begin{tabular}{|c|c|c|}\hline

boys & girls & Total\\\hline

4&5&\textcolor[rgb]{1,0,0}{4+5=9} \\\hline

& &1620\\\hline

\end{tabular}$$

$$\\\textcolor[rgb]{1,0,0}{1620\div 9 = 180} \quad $180 is the multiplication factor$\\

so\\

$number of boys is $4\times 180 = 720 \quad $Put that in the box under the 4$\\

and\\

$number of girls is $5\times 180 = 900 \quad $Put that in the box under the 5$\\\\

$Total number of $ \textcolor[rgb]{0,0,1}{ \;purple\;penguins\;} $ is $ 720+900=1620 $ that checks out very nicely. $

\\\\

$The purple penguins is an insider joke - don't worry if you don't get it - you can google it if you want, then you will know what I am talking about. $$$

Melody
Oct 19, 2014