Anonymous asked in Science & MathematicsMathematics · 9 years ago

How to get the original number using a percentage decrease?

I have statistics for some coursework, and for one year there is 700,000 road accidents, and this was a result of 39% decrease from another previous year, and I don't know how to find the original number, I did get a number which was around 1,800,000 (just under) but I don't believe this is correct...

Any help would be appreciated!

1 Answer

  • 9 years ago
    Favorite Answer

    There is a dead simple way to understand percentages.

    Percentages are hundredths, so you use them as a two digit number after the decimal point, so 0.25 is 25%.

    (OK, 100% is 1.00)

    To add 20%, you multiply by 1.20 to give you the original number (100%) plus 20%.

    To get 18% of a value, multiply by 0.18

    Doing it like this, to reverse any calculation, you divide by the value you originally multiplied by...

    If 700,000 was a reduction of 39%, it is 61% of the original value (100 - 39 = 61).

    So, by the method above, one way of working it out would have been to multiply the original number by 0.61

    To reverse it, divide by 0.61

    700,000 / 0.61 = 1147541 to the nearest integer.

    1,147,541 in a neater format.

    Cross-checking using conventional % on a calculator confirms this.

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