A percent change is a multiplier

A percent decrease tells you what fraction remains

A $15\%$ discount leaves $85\%$ of the original price. An item priced at 72 dollars costs $72(0.85)=61.20$ dollars after the discount. The discount itself is $72(0.15)=10.80$ dollars.

A $20\%$ increase uses $1.2$, not $0.2$. To find an original price from a discounted price of 68 dollars after $15\%$ off, divide: $68/0.85=80$. Multiplying by $1.15$ would answer a different question.

$\displaystyle 72\cdot \left(1-\frac{15}{100}\right)$

The amount after a 15 percent decrease.

$\displaystyle \frac{68}{0.85}$

Recover the amount before a 15 percent decrease.

Each percent change acts on the amount left by the previous one

An increase of $20\%$ followed by a decrease of $20\%$ multiplies the original by $1.2(0.8)=0.96$. The final value is $4\%$ lower, because the second change uses a different starting amount.

A change from $30\%$ to $36\%$ is 6 percentage points, but the relative increase is $(36-30)/30=20\%$. Check which comparison the question requests.

Write conversions so the units cancel

To convert 54 kilometers per hour to meters per second, calculate $54(1000)/3600=15$. Convert both the distance and time units.

For area, square the length conversion factor. If a length in feet is multiplied by $12$ to get inches, an area in square feet is multiplied by $12^2=144$. Desmos handles the arithmetic after you choose the correct relationship.

Keep practicing the connected skills