Formula for percentageThe formula for percentage is the following and it should be easy to use if you follow the straightforward directions given. We will take examples to illustrate.Let us start with the formula on the left An important thing to remember: Cross multiply It means to multiply the numerator of one fraction by the denominator of the other fraction Examples #1: 25 % of 200 is____ In this problem, of = 200, is = ?, and % = 25 We get: is/200 = 25/100 Since is in an unknown, you can replace it by y to make the problem more familiar y/200 = 25/100 Cross multiply to get y × 100 = 200 × 25 y × 100 = 5000 Divide 5000 by 100 to get y Since 5000/100 = 50, y = 50 So, 25 % of 200 is 50 Examples #2: What number is 2% of 50 ? This is just another way of saying 2% of 50 is___ So, set up the proportion as example #1: is/50 = 2/100 Replace is by y and cross multiply to get: y × 100 = 50 × 2 y × 100 = 100 Since 1 × 100 = 100, y = 1 Therefore, 1 is 2 % of 50 Examples #3: 24% of___ is 36 This time, notice that is = 36, but of is missing After you set up the formula, you get: 36/of = 24/100 Replace of by y and cross multiply to get: 36/y = 24/100 y × 24 = 36 × 100 y × 24 = 3600 Divide 3600 by 24 to get y 3600/24 = 150, y = 150 Therefore, 24 % of 150 is 36 Now, we will take examples to illustrate how to use the formula for percentage on the right Examples #4: To use the other formula that says part and whole, just remember the following: The number after of is always the whole The number after is is always the part If I say 25 % of___ is 60, we know that the whole is missing and part = 60 Your proportion will will like this: 60/whole = 25/100 After cross multiplying, we get: whole × 25 = 60 × 100 whole × 25 = 6000 Divide 6000 by 25 to get whole 6000/25 = 240, so whole = 240 Therefore, 25 % of 240 is 60 Examples #5: ___% of 45 is 9 Here whole = 45 and part = 9, but % is missing We get: 9/45 = %/100 Replacing % by x and cross multiplying gives: 9 × 100 = 45 × x 900 = 45 × x Divide 900 by 45 to get x 900/45 = 20, so x = 20 Here we go!. I hope these formula for percentage were helpful. 




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