11. The preferred overall competition area in judo, including the mats, is a square with an area of 256 m2.

a) How do you know that the length and width of the competition area are between 10 m and 20 m?

b) What are the possible last digits of the dimensions if the side lengths are whole numbers? c)

Use your answers to parts (a) and (b) to predict the dimensions.

a) We know that the correct answer will be the square root of 256 since the competition area is a square with an area of 256 meters. And since 10^2 = 100 which is less than 256, the answer has to be greater than 10. And since 20^2 = 400 which is greater than 256, the answer also has to be less than 20. Therefore the answer has to be between 10 and 20. b) The last digit has to be either a 4 or a 6. The units digit is the only digit that will contribute to the units digit of the square. And 0^2 = 0, 1^2 = 1, 2^2 = 4, 3^2 = 9, 4^2 = 16, 5^2 = 25, 6^2 = 36, 7^2 = 49, 8^2 = 64, 9^2 = 81. Of the 10 possible digits, only the values 4 and 6 have a square that has an units digit of 6. c) The square root of 256 based up (a) and (b) above has to be either 14, or 16. So the dimensions are either 14x14 meters or 16x16 meters.