Le Matou matheux: Proportion

The mass concentration

A 60 mL antibiotic bottle has the following note
"Children dose: 5 mL, that is 100 mg of antibiotic".
What is the mass concentration of the product in grammes per litre?

The mass concentration in nitrates of drinking water should not exceed 45 mg/L. A laboratory finds a glass of 12.5 cL full of water, 7 mg of nitrates.

Can we say that this water is drinkable?

A 250 mL drink made of apricot nectar contains 20 g of sugar. This nectar was really too sweet, Antoine adds 33 mL of water.

What is the mass concentration, in grammes per litre, of the new drink?

^{round to the nearest whole number}

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The mass concentration