Which sentence uses the word number correctly in reference to people?

• A. The amount of people reached seven billion.
• B. The number of people reached seven billion.
• C. The number of people reached seven and a half billion.
• D. The amount of people reached seven billion.

Answer: (B)

The key idea here is how we quantify people. People are countable, so we use a number, not an amount. The correct construction is “the number of people” followed by a verb that shows the population size, which is why the sentence reads that the number of people reached seven billion. This clearly communicates a count of individuals.

Using the word amount with people isn’t appropriate because amount is for uncountable quantities, not for discrete items like people.

The version that mentions seven and a half billion is grammatically okay, but in this context the straightforward phrasing with seven billion is the clearest and most standard way to express the milestone.