Article I, 2, of the Constitution requires apportionment of Representatives among the States "according to their respective Numbers." A 1941 federal statute provides that after each decennial census "the method known as the method of equal proportions" shall be used to determine the number of Representatives to which each State is entitled. Application of that method to the 1990 census caused Montana to lose one of its two seats in the House of Representatives. If it had retained both seats, each district would have been closer to the ideal size of a congressional district than the reapportioned single district. The State and several of its officials (hereinafter Montana) sued appropriate federal defendants (hereinafter the Government) in the District Court, alleging, inter alia, that the existing apportionment method violates Article I, 2. A three-judge court, convened pursuant to 28 U.S.C. 2284, granted Montana summary judgment on this claim, holding the statute unconstitutional because the variance between the single districts populatio