What is 45 Percent of 21?
45% of 21 = 9.45
Step by step
- Turn the percentage into a decimal: 45 ÷ 100 = 0.45
- Multiply: 0.45 × 21 = 9.45
How the answer is worked out
“Percent” means “per hundred”, so 45% is 45 out of every 100, or 0.45 as a decimal. Taking 45% of 21 means multiplying 21 by 0.45, which gives 9.45.
9.45 is the 45% share of 21. The remaining 55% is 11.55, and the two parts add back up to 21.
Why calculate this?
Taking a percentage of a number is how discounts, tips, tax and interest are worked out.
- Discounts: 45% off an item priced $21 saves $9.45, so you pay $11.55.
- Tips: a 45% tip on a bill of $21 is $9.45, so the total is $30.45.
- Interest: simple interest of 45% a year on $21 earns $9.45 in one year and $47.25 over five years.
- Tax: a sales tax of 45% on a price of $21 adds $9.45, so the price including tax is $30.45.
A quicker way
Use 10% and 1%: 10% of 21 is 2.1 and 1% is 0.21. 45% is 4 × 10% + 5 × 1% = 8.4 + 1.05 = 9.45.
Swap the numbers if that is easier: 45% of 21 is always the same as 21% of 45, because both are 45 × 21 ÷ 100.
Check the answer
Work backwards: 9.45 ÷ 21 × 100 = 45%. Getting 45% back shows the answer is right.
Rounding
Rounded to a whole number the result is 9, to one decimal place 9.5 and to two decimal places 9.45. Round only at the end: rounding halfway through a calculation can change the last digit.
The formula explained
result = percentage ÷ 100 × number. Dividing the percentage by 100 turns it into a decimal multiplier, so 25% becomes 0.25 and 150% becomes 1.5. Multiplying the number by that decimal gives the share.
Another worked example: 9% of 6
- Turn the percentage into a decimal: 9 ÷ 100 = 0.09
- Multiply: 0.09 × 6 = 0.54
Common percentages of 21
10% of 21 is 2.1, 20% is 4.2, a quarter (25%) is 5.25, half (50%) is 10.5 and three quarters (75%) is 15.75. Knowing these makes it easy to estimate any other percentage of 21 in your head.
Adding and taking away 45%
Increasing 21 by 45% gives 30.45 and decreasing it by 45% gives 11.55. These do not cancel out: raising 21 by 45% and then lowering the result by 45% ends at 16.7475, because the second 45% is taken of a bigger number.
Finding the original number
If 9.45 is 45% of something, divide by 0.45 to get it back: 9.45 ÷ 0.45 = 21. This is how you work out a price before tax or a full amount from a share of it.
Other ways to ask this
The same calculation is often asked in other words. All of these have the answer above:
- What is 45 percent of 21?
- 45% of 21
- 45 percent times 21
- Find 45% of 21
- How much is 45 per cent of 21?
Terms used on this page
- Percentage: the rate, the number with the % sign.
- Base: the number you take the percentage of.
- Decimal multiplier: the percentage divided by 100.
- Mark-up and discount: adding or taking away a percentage of a price.
The answer in other forms
| Result | 9.45 |
|---|---|
| Remaining | 11.55 |
| 45% as decimal | 0.45 |
| 21 + 45% | 30.45 |
Related results
| 5% of 21 | 5% of 21 = 1.05 |
| 10% of 21 | 10% of 21 = 2.1 |
| 15% of 21 | 15% of 21 = 3.15 |
| 20% of 21 | 20% of 21 = 4.2 |
| 25% of 21 | 25% of 21 = 5.25 |
| 50% of 21 | 50% of 21 = 10.5 |
| 75% of 21 | 75% of 21 = 15.75 |
The other way round: 21% of 45
Doing it in a spreadsheet
In Excel, Google Sheets or Numbers type =45%*21 into any cell. Replace the numbers with cell references (for example A1 and B1) to reuse the formula for a whole column.
Common mistakes
Forgetting to divide the percentage by 100 makes the answer 100 times too big. Note that x% of y always equals y% of x.
Practice examples
| 9% of 6 | Show answer9% of 6 = 0.54 |
| 29% of 46 | Show answer29% of 46 = 13.34 |
| 59% of 8 | Show answer59% of 8 = 4.72 |
| 5% of 34 | Show answer5% of 34 = 1.7 |
| 53% of 92 | Show answer53% of 92 = 48.76 |
| 76% of 92 | Show answer76% of 92 = 69.92 |
| 91% of 26 | Show answer91% of 26 = 23.66 |
| 88% of 47 | Show answer88% of 47 = 41.36 |
| 95% of 10 | Show answer95% of 10 = 9.5 |
| 53% of 77 | Show answer53% of 77 = 40.81 |
How this answer was calculated
The result is worked out from the numbers in this page's address when the page is opened, using exact arithmetic wherever possible and rounding only for display. Nothing is copied from a printed table. If you think an answer is wrong, please tell us through the contact page and we will check it.
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Questions
What is 45 Percent of 21?
45% of 21 is 9.45. Formula, steps and practice examples.
What is 45% off 21?
11.55. Taking 45% off leaves 55% of 21.
What is 21 plus 45%?
30.45. Adding 45% is the same as multiplying by 1.45.
What is 45% of 21 as a fraction?
45/100 × 21 = 945/100, which simplifies to 189/20.
How do I find 45% of a number on a calculator?
Multiply the number by 0.45. For 21 that is 21 × 0.45 = 9.45. On many calculators you can also type 21 × 45 %.