bonjour

4.5 milliards = 4.5 x 10 ⁹

1 991 = 1.991 * 10 ³

13.8 milliards = 13.8 * 10 ⁹ = 1.38 * 10 ¹⁰

500 = 5 * 10 ²

- 1 600 = - 1.6 * 10 ³

1 450 = 1.450 * 10 ³