Estimate 58% of 121 by using 10%

58% is about equal to 60%, or 6 times 10%. 10% of 121 is 12.1.

12.1 * 6 = 72.6

To take this further, 58% is 2% less than 60%, or 2 times 1%. 1% of 121 is 1.21.

72.6 - (1.21 * 2) = 72.6 - 2.42 = 70.18