1. Pre-Algebra Using Formulas Lesson 3-4 Suppose you ride your bike 18 miles in 3 hours. Use the formula d = r t to find your average speed. d = r tWrite the formula. 18 = (r )(3)Substitute 18 for d and 3 for t. Divide each side by 3. 18 3 = 3r33r3 Simplify.6 = r Your average speed is 6 mi/h. Additional Examples

2. Pre-Algebra Use the formula F = + 37, where n is the number of chirps a cricket makes in one minute, and F is the temperature in degrees Fahrenheit. Estimate the temperature when a cricket chirps 76 times in a minute. Using Formulas Lesson 3-4 n4n4 The temperature is about 56°F. F = + 37 n4n4 Write the formula. F = + 37 76 4 Replace n with 76. F = 19 + 37Divide. F = 56Add. Additional Examples

3. Pre-Algebra Find the perimeter of a rectangular tabletop with a length of 14.5 in. and width of 8.5 in. Use the formula for the perimeter of a rectangle, P = 2 + 2w. Using Formulas Lesson 3-4 The perimeter of the tabletop is 46 in. P = 2 + 2wWrite the formula. P = 46Add. P = 2(14.5) + 2(8.5)Replace with 14.5 and w with 8.5. P = 29 + 17Multiply. Additional Examples