x^2/25+y^2=1. 2 units is the length of the minor axis, so b, the semi-minor axis, is 2/2=1; width is the length of the major axis, so a, the length of the semi-major axis, is 10/2=5 and the standard equation of an origin-centred ellipse is x^2/a^2+y^2/b^2=1.