A 9 cm long candle burns evenly for 4 hours. How long would a 45 cm long candle take to burn?

6 hours

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9 hours

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15 hours

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20 hours

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Solution

The correct option is D 20 hours
Since the candle burns evenly we need to equate the rates of burning of both the candles.
9 cm candle burns in = 4 hours
Taking Ratio for calculating rate of burning = $\frac{9}{4}$ (cm/hour)
Now assuming the 45 cm candle will take X hours so the rate = $\frac{45}{X}$ (cm/hour)
These two should be same so from equivalent ratio concept
$\frac{9}{4}$ = $\frac{45}{X}$
9X = 45 x 4
X = 20 hours

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