Toán tính nhanh : a) 399 x 45 + 55 x399/ 1995 x 1996 – 1991 x 1995 b) 1996 x 1995 – 996/ 1000 + 1996 x 1994 16/07/2021 By Ruby tính nhanh : a) 399 x 45 + 55 x399/ 1995 x 1996 – 1991 x 1995 b) 1996 x 1995 – 996/ 1000 + 1996 x 1994 c) 637 x 527 – 189/ 526 x 637 + 448 d) 677 X 874 + 251 / 678 X 874 – 623 DẤU / là phần
a) `frac{399 × 45 + 55 × 399}{1995 × 1996 – 1991 × 1995}` = `frac{399 × (45 + 55)}{1995 × (1996 – 1991)}` = `frac{399 × 100}{1995 × 4}` = `frac{399 × 100}{399 × 5 × 4}` $= 4$ b) `frac{1996 × 1995 – 996}{1000 + 1996 × 1994}` = `frac{1996 × (1994 + 1) – 996}{1000 + 1996 × 1994}` = `frac{1996 × 1994 + 1996 – 996}{1000 + 1996 × 1994}` =`frac{1996 × 1994 + 1000}{1000 + 1996 × 1994}` $= 1$ c) `frac{637 x 527 – 189}{526 × 637 + 448}` = `frac{637 . (526 + 1) – 189}{526 . 637 + 448}`= `frac{637 . 526 + 637 – 189}{526 . 637 + 488}`= `frac{637 . 527 + 448}{526 . 637 + 488}`$= 1$ d) `frac{677 × 874 + 251}{678 × 874 – 623}` = `frac{677 × 874 + 251}{(677 + 1) × 874 – 623}` = `frac{677 × 874 + 251}{677 × 874 + 874 – 623}` = `frac{677 × 874 + 251}{678 × 874 + 251}` $= 1$ Trả lời