isabelle/valid/amc12b_2020_p5.thy (13 lines of code) (raw):

(* Authors: Wenda Li *) theory amc12b_2020_p5 imports Complex_Main begin theorem amc12b_2020_p5: fixes a b :: nat assumes "(5::real) / 8 * b - 2 / 3 * a = 7" and "of_nat b - (5::real) / 8 * b - (a - 2 / 3 * a) = 7" shows "a = 42" sorry end