Is there any shortcut to find the % increase or decrease?

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My current salary is $3000$ and now it has become $3450$. The traditional way is to find the difference and divide by the start (base) value to find out the percentage increase.

$\frac{450}{3000}$ which is $15\%$. How can I do so quickly? Sometime the numbers are quite tricky. Is there any other way to do so?

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2 Answers

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Not significantly more quickly in general, but if your base is a nice round number like $3000$, you can "see" it quickly by recognising that it's $100 \times 30$. So to get the percentage increase over a base of $3000$ just involves dividing the increment by $30$. Dividing $450$ by $30$ is generally quicker for most people than doing the full percentage calculation. You can simplify it even more if your increments always come in multiples of $10$, i.e. if the units place is always $0$. Just lop off the $0$ at the end and divide by $3$, i.e. $45$ divide by $3$.

Hope that helped.

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Quoting the answer on Calculating gain percentage:

$\% \text{ Gain} = \dfrac{\text{Price at the end}}{\text{Price at the beginning}} - 1$

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