Sammy made a mistake in the calculation of the time taken by the ladybug. Specifically, he did not properly convert the units for distance and speed. Here's the breakdown of the mistake:
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Unit Consistency: The speed of the ladybug is given in inches per second (3 inches/second), while the distance is given in feet (10 feet). To correctly calculate the time, both measurements need to be in the same units.
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Conversion: There are 12 inches in a foot, so 10 feet is equal to \( 10 \times 12 = 120 \) inches.
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Using the Formula: Sammy correctly rearranged the formula to find time: \[ t = \frac{d}{r} \] but he substituted the distance in feet instead of inches.
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Calculating with Correct Units: \[ t = \frac{120 \text{ inches}}{3 \text{ inches/second}} = 40 \text{ seconds} \]
Thus, the correct time it takes for the ladybug to travel 10 feet at a speed of 3 inches per second is 40 seconds, not 3.3 seconds.