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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

Best Answer 

 #3
avatar+93664 
+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
avatar+17745 
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
avatar+90001 
+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
avatar+93664 
+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

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