Solve any percent problem with one proportion setup
The Percent Proportion
part / whole = percent / 100
This single setup solves three types of percent problems. You always know two of the three values (part, whole, percent) and solve for the third.
Three Types of Problems
Type 1: Find the part — "What is 30% of 80?"
x/80 = 30/100
100x = 2,400
x = 24
Type 2: Find the whole — "15 is 25% of what number?"
15/x = 25/100
25x = 1,500
x = 60
Type 3: Find the percent — "12 is what percent of 48?"
12/48 = x/100
48x = 1,200
x = 25%
How to Identify the Three Values
"of" usually comes before the whole. "is" usually comes before the part. "%" or "percent" identifies the percent.
The unknown is whichever one is missing.
💡 Why this works: Percent means "per hundred." So 30% literally means 30 per 100. The proportion just says: the part relates to the whole the same way the percent relates to 100.
🎯 Practice Problems
1. What is 40% of 90?
A) 36
B) 40
C) 45
D) 54
2. 18 is what percent of 72?
A) 18%
B) 20%
C) 25%
D) 4%
3. 30 is 60% of what number?
A) 18
B) 48
C) 50
D) 180
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🎯 Bonus Practice
1. What is 15% of 200?
A) 15
B) 20
C) 30
D) 35
2. 45 is what percent of 180?
A) 4%
B) 20%
C) 25%
D) 45%
3. 56 is 80% of what number?
A) 44.8
B) 64
C) 70
D) 448
4. A class has 32 students. 8 were absent. What percent were absent?
A) 8%
B) 20%
C) 25%
D) 32%
5. A store marks up items by 40%. If the markup is $28, what was the original cost?