The easiest way to do it (for me) is to find 1% of the regular price. I think we can round the prices to $70,00 and $40,00 to show nice percentage.
70 / 100 = 0,7
So 1% is 0,7. Now we can divide $40,00 by 0,7 to calculate how many percent it is:
40 / 0,7 = 57 (after rounding it to the nearest whole number)
So the discount was 100 - 57 = 43 percent.
Doublecheck (optional):
70 * 57% =
= 70 * 57/100 =
= 7 * 57/10 =
= 7 * 5 7,10 =
= 7 * 5,7 =
= 39,9 (the price after the discount)
70 * 43% =
= 70 * 43/100 =
= 7 * 43/10 =
= 7 * 4 3/10 =
= 7 * 4,3 =
= 30,1 (the value of the discount)
The difference of 0,1 is because of the rounding, but it's correct.