Percent Increase & DecreaseATI TEAS 7 cheat sheet

Change over ORIGINAL

9 key facts 5 practice questions Reviewed Oct 2026

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The Formula

(new − old) / old × 100
The denominator is always the original value
Positive = increase, negative = decrease

Worked

40 → 50: (50−40)/40 = 10/40 = 25% increase
50 → 40: (40−50)/50 = −10/50 = 20% decrease
Same 10 change, different percent — the base changed

The Trap

A 20% rise then a 20% fall does not return to the start
100 → 120 → 96

Shortcut

Increase by 15% = multiply by 1.15; decrease by 15% = 0.85

Key takeaway

Change over ORIGINAL

Before you read

Test yourself first: 5 questions

Question 1 of 5

A patient's temperature rises from 98.6°F to 101.4°F. How many degrees did it increase?

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