A percent is a value divided by 100. For example, 80% and 45% are equal to 80/100 and 45/100, respectively. Just as a percent is a portion of 100, an unknown is part of a whole.
This article focuses on using percent and proportions to solve for that unknown.
Real Life Example
Leslie and seven of her friends celebrate her birthday at Lindsey Street Grill. The restaurant automatically charges a 20% gratuity. If Leslie's meal costs $12.00, how much will she need to tip the server?
What do you know?
The tip amount is 20% or 20 percent. Realize that 20 percent means 20 per 100.
20% = 20/100
The meal costs $12.00
With percents, think part/whole.
20 (part)/100 (whole) = x (the part, or the tip, is unknown)/12 (whole)
20/100 = x/12
Cross multiply. Hint: Write these fractions vertically to get the full understanding of cross multiplying. To cross multiply, take the first fraction's numerator and multiply it by the second fraction's denominator. Then take the second fraction's numerator and multiply it by the first fraction's denominator.
20 * 12 = x * 100
240 = 100x
Divide both sides of the equation by 100 to solve for x.
240/100 = 100x/100
2.4 = x
Verify the answer.
Does 20/100 = 2.4/12?
20/100 = .20
2.4/12 = .20
Leslie will tip the server $2.40.
Practice Exercises
In partnership with Crossroads Restaurant, Archgrove High School is raising money for its school organizations. For five days, Crossroads Restaurant will donate 25% of its profits to a school organization. Use this information to answer the following questions.
Profits
- Sunday: $75,000
- Monday: $62,000
- Tuesday:$68,000
- Wednesday: $96,000
- Thursday: 108,000
1. Student Council will receive 25% of the restaurant's profits from Sunday. How much will Student Council receive?
2. The drill team will receive 25% of the restaurant's profits from Monday. How much will the drill team receive?
3. The band will receive 25% of the restaurant's profits from Tuesday. How much will the band receive?
4. Mu Alpha Theta will receive 25% of the restaurant's profits from Wednesday. How much will Mu Alpha Theta receive?
5. The choir will receive 25% of the restaurant's profits from Sunday. How much will the choir receive?