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## Ratios

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**Ratios**7th Grade Math February, 2011**Ratio**• A ___________ is a comparison of two numbers by division. • A ratio must be expressed in __________ . • Example #1: There are approximately 600 students at Lewisburg School. There are 30 teachers. What is the student to teacher ratio at Lewisburg School? Simplest Form 600/30 or 20/1**3 ways to write a ratio!**• There were 6 chocolate donuts in the box of 12 donuts. • Part to Whole = = ** This can be expressed as: ** 1:2 1 to 2 ALL THREE OF THESE MEAN ~ 1 CHOCOLATE DONUT FOR EVERY 2 DONUTS.**Equivalent Ratios**• Two ratios are the same when put in simplest form. • Example – Are these two ratios equivalent?: • $4 for every 16 ounces $4/16 oz = • $10 for every 40 ounces $10/40 oz = • These two ratios are equivalent!! 1/4 1/4**Choose a partner and take turns taking each others pulse for**2 minutes. • Count the number of beats for each of you. • Write the ratio beats to minutes as a fraction. 1st block**A ___________ is a ratio that compares two different kinds**of units. • Example: • Heartbeat example • Two Units = heartbeats and minutes Rate**Unit Rate**• A ____________ is a ratio that is simplified so that it has a denominator of ONE unit. • Examples: • I made $300 for 6 hours of work. Write the unit rate. • We drove 220 miles on 8 gallons of gas. Write the unit rate 300/6 = 50/1 220/8 = 27.5/1**How to calculate unit rate?**• Easiest way is to divide BOTH the numerator AND the denominator by the denominator. • Example #1:**How to calculate unit rate?**• Easiest way is to divide BOTH the numerator AND the denominator by the denominator. • Example #2:**Grocery Store Comparison – UNIT RATE!**• Four Products: • Find the best price!!**Let’s try together:**http://math.rice.edu/~lanius/proportions/rate.html**Practice**• Small Group: • Number your paper from 1-12 • Deck of cards • LEVEL 0: INDIVIDUAL • Deal out cards evenly to each player • Answer that problem on your paper • Rotate the card (clockwise) to your partner • Continue until you’ve answered all cards • LEVEL 1: PARTNERS • Check your answers with your partners**Practice**• Practice Problems: • Glencoe – Rates and Ratios • Rotate Problems through groups (5-10 minutes) each