The simple, but crude, estimate would be 80*400 = 32000 which is 3.4% off the correct answer of 33129.
I would go for 80 * 410 which is 32800, which is less than 1% off. When multiplying, if you round one number up, you round the other down.
I suggest 80 * 410 = 80 * 400 + 80 * 10 = 32000 + 800 = 32800.
23 percent of 81 is 18.63.
21.06
You do not need to estimate it because it is so easy to work out the exact answer!9*9 = 81 so sqrt(81) = 9 and so 3*sqrt(81) = 3*9 = 27
Their average is 22 and their difference is 9 so use 22 and 9 13*31 = 222 - 92 = 484 - 81 = 403
81*4 = 324
6.9877
81 x 24 = 1944
81 multiplied by 38 is 3,078.
81 3x3x3x3=81
81 multiplied by 324 is 26,244.
569 multiplied by 81 is 46,089.