A friend of mine told me that Samsung's handphone sales in Malaysia rose by 1000% last year. I tried to figure out what 1000% means. This is what I think.
By definition, % increase = (new number-old number)/(old number) x 100
For example, if the old sales figure is 100 and the new figure is 200, then the increase is 100%.
To get 1000%, the new sales figure has to be 1100.
That is, % increase = (1100-100)/100 x 100 = 1000%
Since 1100 is 11 times of 100, therefore a 1000% increase is simply another way of saying 11 times higher. Of course it sounds more impressive to announce that sales has gone up 1000%, than to say it is 11 times more.
Consider these carefully:
While 100% increase means 2 times, a 100% decrease does not mean half. A 100% decrease actually means going down to zero, from whatever number it originally was. Refer to the formula above.
Also, while 100% increase means 2 times, 1000% (which is 10 x 100%) does not mean 20 times. It is actually mathematically 11 times the old number, as explained above.