Order of operations
This calculator follows the standard order of operations, remembered as PEMDAS in the US and BODMAS in the UK: brackets first, then exponents (powers), then multiplication and division from left to right, then addition and subtraction from left to right. So 2 + 3 × 4 is 14, not 20. Many cheap pocket calculators work "immediately", one key at a time, and would show 20; if you need that, add brackets: (2 + 3) × 4.
The famous puzzle 8 ÷ 2(2 + 2) gives 16 here, because implied multiplication is treated like ordinary multiplication and worked left to right. Some textbooks give implied multiplication a higher priority, which gives 1. Writing 8 ÷ (2 × 4) or (8 ÷ 2) × 4 removes the doubt.
How the percent key works
| You type | Result | Meaning |
|---|---|---|
| 200 × 15% | 30 | 15% of 200 |
| 200 + 10% | 220 | Add 10% to 200, for example a price rise or a tip |
| 80 − 25% | 60 | Take 25% off 80, a discount |
| 50% | 0.5 | A percent on its own is divided by 100 |
For reverse percentages and percentage change, the percentage calculator shows the working.
Why 0.1 + 0.2 shows 0.3 here
Computers store numbers in binary, where 0.1 has no exact form, so in most programming languages 0.1 + 0.2 comes out as 0.30000000000000004. This calculator rounds results to 14 significant digits, which removes that noise while keeping far more precision than any real-world sum needs. For money, results are exact to the cent.
Mental math shortcuts
A 15% tip is 10% plus half of that again: on $48, 4.80 + 2.40 = $7.20. To multiply by 5, multiply by 10 and halve. To check a sum, round each number and compare: 49 × 21 is close to 50 × 20 = 1,000, so 1,029 is plausible and 10,290 is not.