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A biologist observes a population of 800 bacteria that doubles every 3 hours. How many bacteria are present after 15 hours?
Number of doubling periods:
\[ 15 \div 3 = 5 \]
Population after 5 doublings:
\[ 800 \times 2^5 = 800 \times 32 = 25,600 \]
#### 25,600
A spacecraft mixture contains fuel and oxidizer in a mass ratio of 3:7. If the total mass of the mixture is 500 kg, how many kilograms of fuel are used?
The total parts in the ratio:
\[ 3 + 7 = 10 \]
Each part mass: