A quantity increases from $600$ to $750$. What is the **percent increase**?

Percent increase $= \dfrac{\text{amount of increase}}{\text{base}} \times 100\%$. The **base** is the **initial** value, $600$. The amount of increase is $750 - 600 = 150$. $\dfrac{150}{600} = \dfrac{1}{4} = 0.25 = 25\%$. - Trap A ($15\%$) reads off $150$ as a percent directly. - Trap B ($20\%$) divides by the new (larger) value $750$ instead of the base — i.e. $150/750 = 20\%$. This is the classic trap: for *percent increase*, divide by the **starting** value, not the ending one. - Trap D ($80\% = 600/750$) is the ratio of old to new, not a percent change. Mirror rule: a *percent decrease* uses the **starting (larger)** value as the base. So if a quantity drops from $750$ back to $600$, the percent decrease is $150/750 = 20\%$ — the same numbers give *different* percentages depending on whether the move is up or down.