To calculated percentage value let’s consider following example.

We have 20 black pebbles and 10 white pebbles; calculate how many percent black pebbles?

$\frac{100\times 20}{30}=\frac{200}{30}=50\frac{4}{3}=66.\mathrm{66\%}$

Formula is

$\frac{100\times \mathrm{Quantity}}{\mathrm{Total}}=\mathrm{\%\; Quantity}$

Formula is

$\frac{100\times \mathrm{Actual\; Increase}}{\mathrm{Initial\; Quantity}}=\mathrm{\%\; Increase}$

In year 2015-16 Rice production was 350 Metric Ton and in year 2016-17 Rice production is expected to be 440 Metric Ton, Calculate % increase in Rice Production.

Initial Quantity is 350 Metric Ton

Actual Increase is 440 - 350 = 90 Metric Ton

% Increase = $\frac{100\times 90}{350}=25.\mathrm{71\%}$

Formula is

$\frac{100\times \mathrm{Actual\; decrease}}{\mathrm{Initial\; Quantity}}=\mathrm{\%\; Decrease}$

In year 2015-16 Cricketer scored 650 runs in ODI and in year 2016-17 Same cricketer scored 560 runs in ODI, Calculate % decrease in runs scored by cricketer.

Initial Quantity is 650 Metric Ton

Actual decrease is 650 - 560 = 110 Runs

% Decrease = $\frac{100\times 110}{650}=16.\mathrm{92\%}$

Formula is

$\frac{X}{(100-X)}\times 100$

Beans prices decreased by 15%, then to keep expenditure constant consumption is increased by how much?

Decrease in price 15%

% Increase in Consumption = $\frac{\mathrm{15}}{(100-\mathrm{15})}\times 100$ = 17.64%