Using Number Sense to Solve Equations

1. 3 – 18 54 –15 = 54False 36 – 18 54 18 = 54False 62 – 18 54 44 = 54False 72 – 18 54 54 = 54True COURSE 2 LESSON 2-2 Using Number Sense to Solve Equations Find the solution of h – 18 = 54: 3, 36, 62, or 72. You can test each number by substituting h in the equation. Since the equation is true when you substitute 72 for h, the solution is 72. 2-2

2. d. = 5 c 6 COURSE 2 LESSON 2-2 Using Number Sense to Solve Equations Use mental math to solve each equation. a.s – 9 = 5 b. 4z = 28 What you think What number minus 9 equals 5? Since 14 – 9 = 5, s = 14. What you think What number times 4 equals 28? Since 4 • 7 = 28, z = 7. c.g + 7 = 11 What you think What number plus 7 equals 11? Since 4 + 7 = 11, g = 4. What you think What number divided by 6 equals 5? Since 30 ÷ 6 = 5, c = 30. 2-2

3. Words crate’s plus contents’ equals total • weight weight weight • Let c = the weight of the contents. • Equation 14.65 + c = 85.21 • 14.65 + c = 85.21 • 14.65 15 85.21 85 Choose compatible numbers. • 15 + c = 85 What number added to 15 is 85? • c = 70 Use mental math. COURSE 2 LESSON 2-2 Using Number Sense to Solve Equations The weight of a packing crate is 14.65 lb. The crate and its contents together weigh 85.21 lb. Estimate the weight of the contents. • The contents of the crate weigh about 70 lb. 2-2

4. s 4 80 t m –61 COURSE 2 LESSON 2-2 Using Number Sense to Solve Equations Solve each equation. Use mental math or estimation. 1.q – 15 = 25 2. 6r = 42 3. 17.25 + s = 21.4 4. = 8 5.m – 39.8 = –101.03 q = 40 r = 7 t = 10 2-2