If a bike travels 7 feet in 1/3 of a second, what is its speed in feet per second?

If a bike travels 7 feet in 1/3 of a second, what is its speed in feet per second?

• A. 7
• B. 21
• C. 3.5
• D. 14

Answer: (B)

Speed is distance per unit of time. When the time is a fraction, divide by that fraction by multiplying by its reciprocal. Here, 7 feet in 1/3 of a second means 7 ÷ (1/3) = 7 × 3 = 21. So the speed is 21 feet per second. Think of it as one full second containing three of these 1/3-second intervals, so the bike would cover 7 feet three times in a second, totaling 21 feet. The other numbers would come from mixing up the operation or the time interval, but with the given values the correct result is 21.

Speed is distance per unit of time. When the time is a fraction, divide by that fraction by multiplying by its reciprocal. Here, 7 feet in 1/3 of a second means 7 ÷ (1/3) = 7 × 3 = 21. So the speed is 21 feet per second. Think of it as one full second containing three of these 1/3-second intervals, so the bike would cover 7 feet three times in a second, totaling 21 feet. The other numbers would come from mixing up the operation or the time interval, but with the given values the correct result is 21.