★ MATH · ARITHMETIC · BASIC CALCULATOR
On the defaults — 100 + 25 × 4 — the answer is 200, and the worked example 12 + 34 × 2 is 80. Tap the keys or type on your keyboard: the calculator works out multiplication and division before addition and subtraction, so 12 + 34 × 2 is 80, not 92. This one is the BASIC tool — four operations, percent and sign, with a button pad — the percentage-calculator page is the PERCENTAGE tool — percent of a number, percent change, percent points — not a general calculator; the fraction-calculator page is the FRACTION tool — fractions with numerators and denominators — not decimals; the add-fractions-calculator page is the ADDITION tool — two fractions added — not a button-pad calculator; and the decimal-to-fraction-converter page is the CONVERTER — decimals to fractions — not arithmetic. No basic calculator exists on this site — this one is the first.
A basic calculator is four operations in the right order: multiplication and division before addition and subtraction. Tap the keys or type — 100 + 25 × 4 is 200 because 25 × 4 is 100 first, then 100 + 100. The % key means out of a hundred, ± flips a sign, C clears everything, CE clears the last number, and ⌫ deletes one character. The answer updates as you type, and the history line keeps the last sum visible.
It means one hundred plus twenty-five fours: 25 × 4 is 100, and 100 + 100 is 200. The expression 100 + 25 × 4 has two operations, and the order matters — multiplication is worked out before addition, so the 25 × 4 is settled first and the answer is 200, not 500. If you added first, 100 + 25 is 125, and 125 × 4 is 500, which is a different sum entirely. The calculator follows the same order every time, so the answer you get is the one the rules of arithmetic give.
Multiplication and division come first. 12 + 34 × 2 is 80, because 34 × 2 is 68 and 12 + 68 is 80 — not 92, which is what you get by chaining left to right. The same rule makes 10 − 2 × 3 equal 4, not 24, and 100 ÷ 4 + 5 equal 30, not 20. If your answer looks too big or too small, the first thing to check is whether a × or ÷ was done after a + or −.
Percent means out of a hundred. 50% is one half, so 200 × 50% is 100, and 25% of 80 is 20. The % key divides the number before it by 100, so 200 × 50% is 200 × 0.5. A common mistake is reading 200 × 50% as 200 × 50, which is 10,000 — the % sign is doing real work, and forgetting it makes the answer a hundred times too big.
Division by zero has no answer. 5 ÷ 0 is not 0 and not infinity — it is undefined, and the calculator says so instead of guessing. The same honesty applies to an empty expression and to an expression that ends with an operator: there is nothing to work out, so the calculator asks for a number instead of inventing one.
On the defaults: work out 100 + 25 × 4, then 12 + 34 × 2.
The defaults are the expression 100 + 25 × 4, which is 200, and the worked example 12 + 34 × 2, which is 80. They are a starting point, not a standard: your sums may be bigger or smaller, positive or negative, and the right answer for you is the one your numbers describe. Tap the keys or type your own expression and the calculator recomputes instantly. Put a sum in, read the answer, and check the working before you use it.
These notes repeat in every explainer section because this page is built to be read start to finish: multiplication and division come first; percent means out of a hundred; and division by zero has no answer.
| Output | Formula | What it means |
|---|---|---|
| Expression | input | 100 + 25 × 4. |
| Result | × ÷ before + − | 200. |
| Result (6dp unrounded) | unrounded to 6dp | 200.000000. |
| Verdict | in words | 100 + 25 × 4 = 200. |
| Reverse: Smallest whole number for n × 4 to reach 100 | step | 25: 25 × 4 = 100. |
| Reverse: Smallest whole number for n + 34 × 2 to reach 100 | step | 32: 32 + 34 × 2 = 100. |
| Reverse: Largest whole number for 100 − n × 3 to stay at 40 or above | step | 20: 100 − 20 × 3 = 40. |
| Reverse: Smallest whole number for n ÷ 4 + 5 to reach 30 | step | 100: 100 ÷ 4 + 5 = 30. |
| Reverse: Largest whole number for 2 × n to stay at 50 or below | step | 25: 2 × 25 = 50. |
| Reverse: Smallest whole number for 200 × n% to reach 100 | step | 50: 200 × 50% = 100. |
| 100 + 25 × 4 | same model | 100 + 25 × 4 = 200. |
| 12 + 34 × 2 | same model | 12 + 34 × 2 = 80. |
| 10 − 2 × 3 | same model | 10 − 2 × 3 = 4. |
| 100 ÷ 4 + 5 | same model | 100 ÷ 4 + 5 = 30. |
| 2 × 3 × 4 | same model | 2 × 3 × 4 = 24. |
| 200 × 50% | same model | 200 × 50% = 100. |
| 7.5 + 2.5 | same model | 7.5 + 2.5 = 10. |
| 1 ÷ 3 | same model | 1 ÷ 3 = 0.333333. |
| 5 × −3 | same model | 5 × −3 = −15. |
| 100 − 25 − 25 | same model | 100 − 25 − 25 = 50. |
| Division by zero | same model | Cannot divide by zero.. |
| Empty expression | same model | Enter an expression.. |
| Trailing operator | same model | The expression ends with an operator — enter a number after it.. |
| 0.1 + 0.2 | same model | 0.1 + 0.2 = 0.3. |
| 1 ÷ 7 | same model | 1 ÷ 7 = 0.142857. |
| 0 × 50% | same model | 0 × 50% = 0. |
| −0 | same model | −0 = 0. |
| 999999999 × 999999999 | same model | 999999999 × 999999999 = 999999998000000001. |
| 5.5 × 2 | same model | 5.5 × 2 = 11. |
| 10 ÷ 4 | same model | 10 ÷ 4 = 2.5. |
| 5 − −3 | same model | 5 − −3 = 8. |
The calculator uses exact fraction arithmetic — numerator and denominator pairs, reduced to lowest terms, never floats — so 0.1 + 0.2 is exactly 0.3, not 0.30000000000000004, and 999999999 × 999999999 is exactly 999999998000000001. The only rounding on the page is the six-decimal display for numbers that never terminate, like 1 ÷ 3 = 0.333333 and 1 ÷ 7 = 0.142857: the stored value is exact and the display stops at six places. What it cannot do is read parentheses — there is no bracket key, so group a sum by working out the bracketed part first — or functions like square roots and powers, which belong on a scientific calculator. It also cannot divide by zero, which has no answer, and it refuses an expression that ends with an operator instead of guessing what you meant.
100 + 25 × 4 = 200. 12 + 34 × 2 = 80. Smallest whole number for n × 4 to reach 100: 25. Smallest whole number for n + 34 × 2 to reach 100: 32. Largest whole number for 100 − n × 3 to stay at 40 or above: 20. Smallest whole number for n ÷ 4 + 5 to reach 30: 100. Largest whole number for 2 × n to stay at 50 or below: 25. Smallest whole number for 200 × n% to reach 100: 50. Source: Bright Side Kit, brightoolbox.com.
Multiplication first: 25 × 4 is 100, then 100 + 100 is 200. Type the expression into the calculator above, or tap the keys, and the answer appears as you type.
Because multiplication comes before addition: 34 × 2 is 68, and 12 + 68 is 80. Chaining left to right gives (12 + 34) × 2 = 92, which breaks the order-of-operations rule.
It divides the number before it by 100: 50% is 0.5, so 200 × 50% is 100. Percent means out of a hundred, and the calculator applies it to the number immediately before the % sign.
C clears the whole expression, CE clears only the last number you entered, and ⌫ deletes one character. Use C to start over, CE to fix the last number, and ⌫ to correct a single slip.
It flips the sign of the last number: 3 becomes −3, and −3 becomes 3. So 5 × −3 is −15, and pressing ± again on −3 gives back 3.
Yes — click the expression box and type: digits, +, −, ×, ÷, %, . and Enter all work. The answer updates as you type, and the on-screen keys do the same thing for touch screens.
Because this calculator uses exact fraction arithmetic, never floats: 0.1 + 0.2 is exactly 0.3. Most calculators store decimals as binary floats, which cannot represent 0.1 exactly; this one stores the fraction 3/10.
The calculator says "Cannot divide by zero" instead of guessing. Division by zero has no answer, so there is nothing honest to display — fix the divisor and try again.