The rule of 70 is used to estimate the time it will take an initial quantity to drop to half its value: 70 : (the decreasing rate) = x ( months ) The decreasing rate = 1 - 0.97 = 0.03 = 3% x = 70 : 3 = 23.33 = 23 1/3 = 23 months and 10 days. Verify: 20 * 0.97^(23.33) = 9.83 ≈ 10
The <em>change in y</em> is the difference in y-coordinates between the lower right point and the upper left point. Similarly, the <em>change in x</em> is the difference in the x-coordinates of those points.
