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# Ratios and proportions power point copy

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### Ratios and proportions power point copy

1. 2. <ul><li>We use ratios to make comparisons between two things. When we express ratios in words, we use the word &quot;to&quot; -- we say &quot;the ratio of something to something else&quot; -- for example, the ratio of squares to triangles in the illustration below. Ratios can be written in several different ways. As a fraction 1⁄2, Using the word to, and a colon 1:2 </li></ul>
2. 4. <ul><li>Jeannine has a bag with 3 videocassettes, 4 marbles, 7 books, and 1 orange. </li></ul><ul><li>1) What is the ratio of books to marbles? </li></ul><ul><li>2) What is the ratio of videocassettes to the total number of items in the bag? </li></ul>
3. 5. <ul><li>1)Expressed as a fraction, with the numerator equal to the first quantity and the denominator equal to the second, the answer would be 7/4. Two other ways of writing the ratio are 7 to 4, and 7:4. </li></ul><ul><li>2) There are 3 videocassettes, and 3 + 4 + 7 + 1 = 15 items total. The answer can be expressed as 3/15, 3 to 15, or 3:15. </li></ul>
4. 6. <ul><li>A proportion is an equation with a ratio on each side. It is a statement that two ratios are equal. 3/4 = 6/8 is an example of a proportion. </li></ul><ul><li>When one of the four numbers in a proportion is unknown, cross products may be used to find the unknown number. This is called solving the proportion. Question marks or letters are frequently used in place of the unknown number. </li></ul>
5. 7. <ul><li>1:2=12:24 </li></ul><ul><li>3 to 5=9 to 15 </li></ul><ul><li>1/3=3/9 </li></ul><ul><li>Solve for n: 1/2 =  n /4. Using cross products we see that 2 ×  n  = 1 × 4 =4, so 2 ×  n  = 4. Dividing both sides by 2, n  = 4 ÷ 2 so that n  = 2. </li></ul>
6. 8. <ul><li>Key: Mary has 2 pencils,3 pens and 5 markers. </li></ul><ul><li>What is the Ratio of pencils to pens? </li></ul>