45 billion
45:191
100 000 x 459.00 = 45 900 000
145,500
45%
450 km
45,045,000
455,000,000,000 = 4.55 x 101145.5000 000 000 = 4.55 x 101
Brussels capital region has 160km² greenspace occupy 80km² but more than 40% of this green space is private (gardens, royal domaine) => 45 km² of pulic greenspace for 1 million inhabitants => 45 000 000 m²/ 1 000 000 answer is 45m² per inhabitant... not so bad :)
45 000 x 27 =1 215 000
45,000,000 in scientific notation is 4.5 x 107.
Exactly as you have done in the question.