Core Focus on Rational Numbers & Equations Subtracting Rational Numbers Lesson 3.3

Warm-Up Find the value of each expression. 1.−3 − − (−5) 3.−235 − − –7 15 –345 –36.9

Subtracting Rational Numbers Subtract positive and negative fractions and decimals. Lesson 3.3

Subtracting Positive and Negative Numbers 1.Turn the subtraction symbol into an addition symbol by adding the opposite. 2.Follow the rules for adding fractions and decimals to determine the sum.

Find the difference in each situation. Step 1Yoko had $34.86 in her checking account. She wrote a check that left her with a balance of −$ Find the value of the check she wrote. Step 2The neighborhood bank was offering savings accounts in January that earn interest. In February, the interest rate dropped to. What number represents the interest rate change from January to February? Step 3Margaret found out that the lowest temperature ever recorded in Vermont was −50.1° F. The highest temperature ever recorded in Vermont is 105.1° F. What is the difference between these two temperatures?

Step 5What would you consider the most important thing to remember when adding positive and negative fractions or decimals? Why? Step 4R.J. dove into the ocean and reached an elevation of feet (the distance below sea level). On his second dive, he reached an elevation of feet. What was the difference between his two dives?

Example 1 Find the value of. Change the subtraction symbol to an addition symbol by adding the opposite Convert each mixed number to an improper fraction Create equivalent fractions using the least common denominator of 6. Rewrite the expression with equivalent fractions. Add the numerators. Simplify

Example 2 Bromine has a boiling point of 58.8º C and a melting point of –7.2º C. What is the difference between the boiling point and the melting point? Write the expression to represent the situation: Add the opposite: Add by lining up the decimals. The difference between the boiling point and melting point of Bromine is 66º C – (–7.2)

Communication Prompt Science and math are related in many ways. What is one way you have observed that math and science overlap?

Exit Problems Find each difference − (−2.8)