1. 348 ≈ 350; 423 ≈ 420; 2743 ≈ 2740; 17246 ≈ 17250; 429895 ≈ 429900. 2. 7167 ≈ 7200; 1243 ≈ 1200; 6417 ≈ 6400; 1462 ≈ 1500; 55555 ≈ 55600. 3. 6235 ≈ 6000; 231681 ≈ 232000; 3864 ≈ 4000; 76431 ≈ 76000; 149702 ≈ 150000. 4. 33569243 ≈ 34000000; 4011997 ≈ 4000000; 79598765 ≈ 80000000.