Le Matou matheux: percentages

Finding a percent or a piece of information

An item increases by12% and costs now 313.60 €.
How much did it cost before the the increase?

€

An item decreases by 12% and costs now 237.60 €.
How much did it cost before the decrease?

€

The dimensions of a rectangular are increased by 10%.

What is the percentage with which its perimeter increases? and its area ?

A population increases by 10% during a year
and decreases by 10% the year after.

After two years, the population

The percentage is