The first concept that kids must understand is the idea of percentage. Percent is a ratio or fraction that is part of a whole. Teaching percent is a continuation of using fractions. A fraction is a percentage of a whole. Use the example of a pizza. If two boys both at half of a pizza they both ate 50 percent. To find the percent, take the fractional part and divide the numerator by the denominator. For example, 1/2 is 1 divided by 2, which equals .5. We then move the decimal two places to the right to get 50 percent.
Use pieces of candy to teach percent also. Give students a handful of candy and have each count out how many they have. Add the total pieces of candy to find the denominator while each student uses the number of pieces he has as the numerator. By dividing the numerator by the denominator the students will find out the percentage of candy that they received of the entire bag of candy.
The easiest percent to teach is 10. 10 percent of 100 is 10. 10 percent of 200 is 20. Show students that when they need to figure out 10 percent, they simply need to move the decimal one place to the left. They can then use this to figure out other simple percentages. If they know that 10 percent of 40 is 4, they can then figure out 30 percent by multiplying 4 times 3 (for 30 percent). 30 percent of 40 is 12.
Make finding tens a little harder by giving the students different numbers. Have them find 10 percent of 35 (3.5) or 82 (8.2). Ask them if they can see the pattern when finding 10 percent.
Teaching percent of increase is a good place to start hitting a little economics as well. Keep it simple, though. As the years pass, inflation happens and most items go up in price. Gas is one of those items that kids probably hear their parents discussing. Give students similar problems as the following: in 2000 the average gas prices were about $1.52 per gallon. The cost of gasoline in 2010 was about $2.67. To find the percent of increase find the difference between the two and then divide the difference by the original. Subtract 1.52 from 2.67. The difference is 1.15. Now divide 1.15 by 1.52 which is .7565, making the answer a 76 percent increase. Notice that when the third number past the decimal is 5 or higher the second number is rounded up.
Another percent of increase problem can involve taxes. Give the students the problem that in 2000 the Smith family paid 15 percent of their income to taxes. In 2001 they needed to pay 18 percent. Both years the family made $54,000. Find the amount of tax they paid each year and then find the percent of increase. In 2000 they paid $8,100 and in 2001 they paid $9,720. The percent of increase is 20 percent.
Shopping is something that is beginning to interest fourth-grade students. This is a good place to teach about percent of decrease or how much an item has been reduced or gone down in price.
Say that one of the boys in the class wants a video game. The original price is $60, but it is on sale at a discount of 20 percent. Have the students find the amount of decrease. They will multiply 60 by 20 percent (.2), which is 12. Subtract 12 from 60 to find the sale price of $48.
Another problem can involve a girl student. She has been waiting for a pair of shoes to go on sale. They were originally $43. They are now on sale for $35. Have the students find the percent of decrease by finding the difference, which is 8. Eight divided by 43 is .186, which would be 19 percent.