1 5 - ( 7 - 3 ) = 2 ( 7 + 3 ) / 5 = 3 ( 7 + 5 ) / 3 = 4 7 - 5 + 3 = 5 3 x ( 7 - 5 ) = 6 5 x 3 - 7 = 7 5 - 3 + 7 = 8 7 x ( 5 - 3 ) = 9 7 + 5 + 3 = 10 3 x 7 - 5 = 11 ( 7 - 3 ) x 5 = 12 3 x 5 + 7 = 13 3 x 7 + 5 = 14 7 x 5 - 3 = 15 3 x ( 7 + 5 ) = 16 3 + 7 x 5 = 17 ( 3 + 7 ) x 5 = 18 ( 3 + 5 ) x 7 = 19 3 x 5 x 7 = 20 3^(5–3) x 7 =