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For solving such questions we need to know ratio and proportion .
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We know that in a : b : c = x : y : z ;
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a : b = x : y
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b : c = y : z
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c : a = z : x
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let the unknown value be x and y ;
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Therefore ;
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Required ratio = 6 : x : 15 = y : 20 : 10
➠ x : 15 = 20 : 10
Now, we will change it into fraction
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➠ x / 15 = 20 / 10
➠ x = 20 × 15 / 10
➠ x = 2 × 15
➠ x = 30
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Now the ratio becomes ;
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6 : 30 : 15 = y : 20 : 10
➠ 6 : 30 = y : 20
➠ 6 / 30 = y / 20
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➠ y = 6 × 20 / 30
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➠ y = 6 × 2 / 3
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➠ y = 2 × 2
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➠ y = 4
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[tex]\sf{\underline{\boxed{\large{\blue{\mathsf{Required \: ratio = 6 : 30 : 15 = 4 : 20 : 10 }}}}}}[/tex]
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