# Numbers representation, tolerance and precision

## Integers

WIRIS does calculations in exact mode, and only falls to approximate mode when any decimal number is involved. A decimal number is a number that has a decimal mark. A number without decimal mark is an integer. Examples of exact expressions that are not integer numbers are: , , , ...

You can convert an exact expression to approximate by making a simple operation with a decimal number, like multiply by 1.0.

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Beware that, despite the correct answer beeing an integer, the student can always answer a decimal number close enough, and it will be graded as correct. If you want to force the student to answer an integer, you better set *Integer form*.

Also note some WIRIS commands sometimes return an exact number and sometimes an approximate one. For example: `atan()`

, `integrate()`

, `solve()`

,... Keep this in mind when programming the algorithm in *Variables*.

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## Decimal numbers

A decimal number is a number that has a decimal mark. Decimal numbers are shown using *Precision* setting, and are compared using *Tolerance* setting. What is understood as decimal mark depends on the modes *General* and *Quantity*.

- General: Decimal mark is exclusively the dot. Decimal mark must be inside the number, not at sides; leading and trailing decimal marks are not allowed.
- Quantity: By default, all dots, commas and apostrophes are understood as decimal marks. Leading and trailing decimal marks are allowed.

## Precision

Precision is the number of significant figures or decimal places of variables shown after calculations. That is, calculations are made internally with full precision, and at the end they are rounded to the set precision. Precision affects the decimal numbers shown in wordings, feedback, and so. Max precision is 15. When rounding, the rule used for tie-breaking is half-up.

Consider the number 12.345

Precision | Rounded to significant figures | Rounded to decimal places |
---|---|---|

6 | 12.345 | 12.345000 |

5 | 12.345 | 12.34500 |

4 | 12.35 | 12.3450 |

3 | 12.3 | 12.345 |

2 | 12 | 12.35 |

1 | 12 | 12.3 |

Precision is not the allowed deviation between student and correct answers; that is Tolerance. But precision can have a bad impact in the comparison, if set improperly. Precision affects the correct answer, how it's shown to the student, but also the actual value. The student answer will be compared with the correct answer, that has been rounded using precision. If precision number is smaller than tolerance number, then good student answers will probably be graded as bad. That's because if the precision number is small, then the correct answer will be rounded too much, probably outside the tolerance range. So remember to set the precision number always greater than the tolerance number. Also note the precision does relate approximately with the relative tolerance, but does not relate directly to the absolute tolerance. There is a warning about this point.

## Tolerance

*Tolerance* number is used to compare the student answer and the *Correct answer*. Denote by the student's answer, the correct answer, and the tolerance.

### Percent error

The student answer has an error margin with respect to the correct answer. An answer will be marked as correct if it satisfies

For instance, if the correct answer is

Percent error | Interval of acceptance |
---|---|

10 | |

1 | |

0.1 | |

0.01 |

### Absolute error

The student answer has a margin of error of . An answer will be marked as correct if it satisfies

For instance, if the correct answer is

Absolute error | Interval of acceptance |
---|---|

1 | |

0.1 | |

0.01 | |

0.001 |

### Significant figures

Check that the first significant figures of student and correct answers are identical. An answer will be marked as correct if it satisfies

where is such that , and is the truncation function.

For instance, if the correct answer is

Student answer | ||||
---|---|---|---|---|

Significant figures | 20.01 | 19.6 | 19.59 | 19.58 |

1 | ||||

2 | ||||

3 | ||||

4 |

### Decimal places

Check that the first decimal places of student and correct answers are identical. An answer will be marked as correct if it satisfies

where is the truncation function. For instance, if the correct answer is

Student answer | ||||
---|---|---|---|---|

Decimal places | 19.6 | 19.59 | 19.587 | 19.586 |

1 | ||||

2 | ||||

3 |

## Notation

These notations apply only to decimal numbers. Numbers and expressions without a decimal point in them are exact, and so these notations don't apply to them. You can always convert an exact expression to decimal by multiplying by `1.0`

for instance.

### Auto

`Auto`

is the default notation if you use *significant figures* in Precision setting. `Auto`

notation chooses the best format for wach type of values: most numbers are shown without changes but very big or small ones are shown in scientific notation. Decimal trailing zeros are removed too.

If you are using significant digits as precision, the floating number will be shown in scientific notation when or . Note that this does not apply to integer numbers.

### Decimal

`Decimal`

notation is like `Auto`

but never shows scientific notation. Note that this notation can produce numbers with lots of digits. For example, you will see in *Algorithm*, but you will get actually a long number of hundred digits.

This is the only option when working with *decimal places* as precision.

### Scientific notation

`Scientific notation`

always shows numbers in normalized scientific notation, also called exponential notation.

Precision number here means significant digits of the mantissa to show.

Consider as correct answer. In *General mode* as allowed input, the only accepted notation is . If you want to allow students answering in other formats you must use *Quantity* in *Validation > Allowed input* setting instead. This way is also accepted. To allow the lowercase *e*, untick its box in *Validation > Options for quantity > Constants*.

Note that the following answers are not OK:

- 12.3e+2: because there are too many digits before the decimal point
- 1.0 e+2: because there is an extra space in the middle

## Concrete number of decimals as assertion

As any other assertion, we can choose if the student answer has a concrete number of significant figures or decimal places.

Imagine that we want the student to ask with 1 number after the decimal point. Suppose that the correct answer is 21.5, then

## Repeating decimals

WIRIS Quizzes understands decimal numbers with repeating decimals. **Repeating decimals** is a notation used to represent decimal numbers with periodic expansion, that is, rational numbers. There are 3 symbols available to mark repeating decimals; you can use any of them. The system is smart enough to know that , and of course that .

### What questions can we do today?

#### Students can answer numbers with repeating decimals at any time

Students can answer numbers with repeating decimals at any time. The system will recognize it like any other decimal number. If the answer fits the*Validation*criteria (

*Tolerance, Mathematically equal*, ...) then it will be graded as

*Correct*.

#### Constant number with repeating decimals

Teachers can set for a*Correct answer*a constant number with repeating decimals. The student can answer any number, with or without repeating decimals, even a fraction, and it can be graded as correct, depending on the

*Validation*criteria.

#### Use of "Literally equal"

At present there is no*Additional property*to validate if a student answer has or has not repeating decimals. But you can use

*Literally equal*to check if the student answer and the correct answer have the same form, that is, if they both have or have not repeating decimals.

#### Repeating decimals

At present you can not generate variables with repeating decimals.LIVE DEMO