Q. Find the fourth proportional to 5, 9, 12, ….
Answer: 21.6
Notes: Let the fourth proportional to 5, 9, 12 be x. Then 5:9::12:x<=>$latex 5\times x=9\times 12 $ $latex =>x=\frac{9\times 12}{5}=21.6&s=2$ Hence the fourth proportional to 5, 9, 12 is 21.6

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