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Mathematics

If (x - 9) : (3x + 6) is the duplicate ratio of 4 : 9, find the value of x.

Ratio Proportion

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Answer

Duplicate ratio of 4 : 9 = 42 : 92 = 16 : 81.

According to question,

(x - 9) : (3x + 6) = 16 : 81

x93x+6=168181(x9)=16(3x+6)81x729=48x+9681x48x=96+72933x=825x=82533x=25.\Rightarrow \dfrac{x - 9}{3x + 6} = \dfrac{16}{81} \\[0.5em] \Rightarrow 81(x - 9) = 16(3x + 6) \\[0.5em] \Rightarrow 81x - 729 = 48x + 96 \\[0.5em] \Rightarrow 81x - 48x = 96 + 729 \\[0.5em] \Rightarrow 33x = 825 \\[0.5em] \Rightarrow x = \dfrac{825}{33} \\[0.5em] x = 25.

Hence, the value of x is 25.

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