Percent as Rate per Hundred

Percent is a special ratio that always compares a part to the number one hundred. The word percent literally means "per hundred". When you read 25%, you are reading "25 out of 100". Percents show up everywhere — battery levels, quiz scores, sales tags, sports stats — because comparing to 100 makes very different totals easy to talk about.

The Percent Symbol

• The symbol % means "out of 100". It is short for "per centum" — Latin for "by the hundred".
• 25% means 25 out of every 100. Half a group is 50% of the group.
• A whole, complete amount is 100% — every single one of the 100 parts.
• 0% means none of the parts; the symbol still uses the "/100" idea.

Modeling Percent on a 10 by 10 Grid

• Draw or use a 10x10 grid. The grid has exactly 100 small squares — one square = 1%.
• To show 25%, shade any 25 of the 100 squares. The shaded part is one quarter of the grid.
• To show 50%, shade 50 squares — exactly half the grid.
• To show 75%, shade 75 squares — three quarters of the grid.
• To show 100%, shade every square. Nothing is left unshaded.

Percent, Fraction, Decimal

• Every percent has a matching fraction with denominator 100: 25% = 25/100, 7% = 7/100.
• Every percent has a matching decimal — divide by 100 (shift the decimal point two places left): 25% = 0.25, 7% = 0.07.
• To go from a decimal back to a percent, multiply by 100 (shift two places right): 0.6 = 60%.
• A fraction over 100 is already a percent: 40/100 = 40%.

Reading Everyday Percents

• 50% off — half price; pay 50 of every 100 cents.
• A battery at 30% — 30 of every 100 charge units left.
• A quiz score of 90% — 90 questions correct out of every 100.
• 100% complete — the whole job is finished, none of the 100 parts left undone.