**Problem 1A-1:** Average Speed

At time t = 0 a car starts to move from point A along a horizontal line across as shown in the picture. Three more measuring points, B, C and D are set up along the line. The distances of those additional points from point A and the time when the car passes them are tabulated as follows:

Measuring points | A | B | C | D |
---|---|---|---|---|

Distance from point A, in kilometers (km) | 0.00 | 0.10 | 0.50 | 1.50 |

Time the car passes, in minutes (min) | 0.00 | 0.50 | 1.50 | 3.00 |

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**Solution:**

Speed is defined as distance ÷ time.

The average speed from A to B = (0.10 - 0 km)÷(0.50 - 0 min) = (0.10 km)÷(0.50 min) = 0.20 km/min = (0.10 km)÷((0.50 min)÷(60 min/hr)) = (0.1×60÷0.50 km/hr) = 12.0 km/hr = ((12.0 km/hr)÷(1.61 km/mile)) =7.45 mile/hr. The average speed from C to D = (1.50 - 0.50 km)÷(3.00 - 1.50 min) = (1.00 km)÷(1.50 min) = 0.67 km/min. = (1.00 km)÷((1.50 min)÷(60 min/hr)) = (1.00×60÷1.50 km/hr) = 40.0 km/hr. = ((40.0 km/hr)÷(1.61 km/mile)) =24.8 mile/hr.

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