If you multiply a number by 100%, you are simply multiplying by 1. You can multiply by 100% to change a decimal number or fraction to a percent. (0.25)(100%)=25%. You can also divide by 100% to change a percent to a decimal number. 65%/100%= 65/100 or 0.65. This is a complete lesson with a video & exercises showing, first of all, the common shortcut for multiplying & dividing decimals by powers of ten: you move the decimal point as many steps as there are zeros in the number 10, 100, 1000 etc. Then, I also show where this shortcut originates, using place value charts. In reality, the decimal point moving is sort of an illusion, and instead, the digits of the number move within the place value chart. This explanation can really help students to understand the reason behind the "trick" of moving the decimal point. The lesson below explains the shortcut in more detail, plus has different kinds of exercises, word problems, and even a fun riddle for students.
1. Multiply.
2. Let's practice some more.
3. Now let's practice using powers of ten.
4. Divide.
5. Now let's practice using powers of ten.
6. Divide. Think of fractions to decimals, or use the shortcut. Compare the problems in each box! 7. A 10-lb sack of nuts costs $72. 8. Find the price of 100 ping-pong balls if one ping pong ball costs $0.89.
9. Divide whole numbers by 1000. Simplify the final answer by dropping any ending decimal zeros.
10. Divide whole numbers by 10 and 100. 11. Find one-tenth of... a. $8 b. $25.50 c. $126 12. Find one-hundredth of... a. $78 b. $4 c. $390 13. A pair of shoes that cost $29 was discounted by 3/10 of its price. What is the new price?(Hint: First find 1/10 of the price.) 14. Find the discounted price: a. A bike that costs $126 is discounted by 2/10 of its price. b. A $45 cell phone is discounted by 5/100 of its price. 15. One-hundredth of a certain number is 0.03. What is the number? 16. Which vacuum cleaner ends up being cheaper? Model A, with the initial price $86.90, is discounted by 3/10 of its price. Model B costs $75 now, but you will get a discount of 1/4 of its price.
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