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Jack
10-10-2013, 11:15 AM
How can we find the ratio of x+21 to y+21 if we know the ratio of x to y is 5:2 and the ratio of x+4 to y+4 is 7:4?

miranda
10-10-2013, 11:16 AM
The ratio of x to y is 5:2 means
\frac{x}{y}=\frac{5}{2} \Rightarrow 2x=5y
The ratio of x+4 to y+4 is 7:4 means
\frac{x+4}{y+4}=\frac{7}{4} \Rightarrow 4(x+4)=7(y+4) [/tex]
\Rightarrow 4x=7y+28-16 \Rightarrow 4x=7y+12 \Rightarrow 2(2x)=7y+12
\Rightarrow 2(5y)=7y+12 \Rightarrow 10y=7y+12 \Rightarrow 3y=12 \Rightarrow y=4
and
2x=5(4) \Rightarrow x=10

Therefore the ratio of x+21 to y+21 will be given by the following expression
\frac{x+21}{y+21}=\frac{10+21}{4+21}=\frac{31}{25}

Jack
10-10-2013, 11:16 AM
Thank you very much!!:)