Decimal
0.15 × 30 = 4.5
Fraction
— (no clean fraction)
Equation
(15 ÷ 100) × 30 = 4.5
How to calculate 15% of 30
Two steps — convert to a decimal, then multiply.
- 1
Convert the percentage to a decimal
15 ÷ 100 = 0.15
- 2
Multiply the original number by the decimal
0.15 × 30 = 4.5
Where 15% of 30 comes up in practice
A 15% tip on a $30 restaurant bill comes out to $4.50, bringing the total to $34.50.
How to read this number
- 15% is the long-running US baseline for adequate restaurant service. A $4.50 tip on a $30.00 bill brings the total to $34.50.
Mental math shortcut
10% + half of 10% (15% = 1.5 × 10%).
The same calculation, expressed three ways
Knowing one of these gives you the other two — handy when a problem is phrased differently to what you typed.
- 4.5 is 15% of 30
- 4.5 out of 30 = 15%
- 15% off $30.00 = $25.50
Frequently asked
Common follow-up questions for 15% of 30.
Yes — multiplying by the decimal form (0.15) is exactly what "15% of 30" means. 30 × 0.15 = 4.5.
No — 15% of $30 is the discount amount itself ($4.50). 15% off $30 means the sale price is $25.50 (the original price minus the discount).
10% + half of 10% (15% = 1.5 × 10%). For 15% of 30 that gives 4.5 directly.
The number is 30. To work it out, divide 4.5 by 0.15: 4.5 ÷ 0.15 = 30.
Total = $34.50. The bill ($30) plus a 15% tip ($4.50) = $34.50.
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