The area of an ellipse is given by A = πab where a is half the major axis = 20/2 = 10 and b is half the minor axis = 10/2 = 5. Taking pi = 3.142, we have A = 3.142 x 10 x 5 = 157.079 m^2 = 157 m^2 to the nearest whole number. Therefore, the area of an ellipse with the major axis 20 m and the minor axis 10 m = 157 square meter to the nearest whole number.