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Why 1.5 Hours, 5.6 Feet and 4.3 Overs Can Mislead

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A Peek Beyond the Point · Misleading decimal notation · 3:19

You'll learn: Clock time, feet and inches, and cricket overs group by 60, 12 and 6, not 10, so writing them with a dot like a decimal misleads.

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Why 1.5 Hours, 5.6 Feet and 4.3 Overs Can Mislead

3:19

Playing

Why 1.5 Hours, 5.6 Feet and 4.3 Overs Can Mislead

You'll learn: Clock time, feet and inches, and cricket overs group by 60, 12 and 6, not 10, so writing them with a dot like a decimal misleads.

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Misleading decimal notation

1

Spot Decimal-Point and Unit Errors
3:24
Spot Decimal-Point and Unit Errors
You'll learn: A misplaced point or a mixed unit changes a value by a factor of ten or more; check both.

Next topic

Simple fractions as decimals

2

Write Halves, Quarters and Fifths as Decimals
3:19
Write Halves, Quarters and Fifths as Decimals
You'll learn: Rewrite halves, quarters and fifths with denominators 10 or 100 to get their decimals.
Separate a Decimal's Whole and Fractional Parts
3:29
Separate a Decimal's Whole and Fractional Parts
You'll learn: Every decimal has a whole part and a fractional part separated by the point.

Next topic

Letters representing numbers

2

How Can a Letter Stand for a Changing or Unknown Number?
3:04
How Can a Letter Stand for a Changing or Unknown Number?
You'll learn: A letter can stand for a quantity that changes or for one we don't know yet.
Describe a Number Relationship with Letters
3:10
Describe a Number Relationship with Letters
You'll learn: Translate a number relationship described in words into an expression with letters.

Next topic

Formulas from quantities

3

Write a Formula for a Total Cost
3:09
Write a Formula for a Total Cost
You'll learn: Write a formula for total cost as price times quantity.
Express an Age Relationship with a Letter
3:04
Express an Age Relationship with a Letter
You'll learn: Write one person's age in terms of another's using a letter.
Write Perimeter Formulas for Regular Shapes
3:09
Write Perimeter Formulas for Regular Shapes
You'll learn: The perimeter of a regular shape is the number of sides times the side length.

Next topic

Calendar and number-grid relationships

2

Write Relative Values in a Calendar or Number Grid
3:03
Write Relative Values in a Calendar or Number Grid
You'll learn: Write every cell of a calendar or grid block relative to one cell, using row and column rules.
Why Do the Diagonal Sums Match in a Number Grid?
3:17
Why Do the Diagonal Sums Match in a Number Grid?
You'll learn: Using a letter for one corner shows both diagonal sums are always equal.

Next topic

Evaluating algebraic expressions

2

Substitute a Number Without Changing the Expression's Structure
3:03
Substitute a Number Without Changing the Expression's Structure
You'll learn: Replace the letter with a number but keep every operation of the expression unchanged.
How Does an Expression's Value Change with Its Input?
3:17
How Does an Expression's Value Change with Its Input?
You'll learn: Substitute different inputs to see how the value of an expression changes.

Next topic

Angles at an intersection

2

Why Do Adjacent Angles on a Line Add to 180°?
3:04
Why Do Adjacent Angles on a Line Add to 180°?
You'll learn: Adjacent angles that form a straight line together make 180°.
Why Are Vertically Opposite Angles Equal?
3:10
Why Are Vertically Opposite Angles Equal?
You'll learn: A single equality proof needs the linear-pair deductions to remain visible.

Next topic

Geometric facts versus measurements

1

Why Does Measuring a Diagram Not Prove a Geometric Fact?
3:38
Why Does Measuring a Diagram Not Prove a Geometric Fact?
You'll learn: Measuring a drawing can suggest a fact, but drawings are imperfect, so a proof is needed.