Pinewood Derby Q&A

Math, rates - can someone check my math?

We have to determine the averages of Pine Wood Derby cars.... yeah.... They take 3 trials, solve all the problems with the data given. The cars had to go 240cm. Trial: | Time: | Average Speed (cm/s) 1 | 8.0 | __________________ 2 | 10.0 | __________________ 3 | 8.0 | __________________ -------------------------------------------------------- Questions: 1. Complete the third column of the chart, show your work. I got.. Trial: | Time: | Average Speed (cm/s) 1 | 8.0 | 240/8 = 30cm/s 2 | 10.0 | 240/10 = 24cm/s 3 | 8.0 | 240/8 = 30cm/s -------------------------------------------------------- 2. What was the overall average speed of the car? Show your work. 8+10+8 = 26 26/3 = 8.6666 (go only four places) 240/8.6666 = 27.6923cm/s Average speed = 27.6923 ---------------- 3. Another car has an average speed of 25cm/s. If the rate could be increased by 10% what would the... new average speed be? Show your work. .10 * 25 = 2.5 2.5 + 25 = 27.5 new average = 27.5cm/s --------------------- 4. The car's speed is actually increased to 29.5cm/s. What was the percent of increase? show your work. ...........Here I guessed and checked. first: .15 * 25 = 3.75 25 + 3.75 = 28.75 X then... .18 * 25 = 4.5 4.5 + 25 = 29.5 CORRECT But is there a mathematical way to get this answer besides guess and check? this is counted as two quiz grades so I want to be sure I got these right.

Public Comments

1. You're correct. For q/ The car's speed is actually increased to 29.5cm/s. What was the percent of increase? show your work. Work out the increase, then work out the percentage. The increase is 29.5 - 25 = 4.5. The percentage is increase / base = 4.5 / 25 = 0.18 = 18%