Learn French: Dans un siècle, la population augmentera. - In a century, the population will increase.

Because 'in a century' is a distant time and this is a prediction, French uses the futur simple (augmentera). The futur proche (va augmenter) is typically reserved for events happening very soon or that are highly certain and already set in motion.

How do you form the futur simple for this verb?

For regular -er verbs like augmenter (to increase), you take the full infinitive (dictionary) form of the verb and simply add the future endings. Since la population is a singular noun taking the elle (she/it) form, we add the ending -a to augmenter, creating augmentera.

Why does this sentence use dans for 'in'? Could I use en?

When talking about a specific point in the future when an event will begin or happen (like 'in a century from now'), you must use dans. The preposition en is used for 'in' only when discussing the duration of time it takes to complete an action.

Even though la population refers to many people, why is the verb singular?

In French, collective nouns like la population or la famille are grammatically singular. You treat them exactly like elle (she/it), which is why the verb uses the singular ending (augmentera) rather than a plural one.