IELTS Academic Writing Task 1 Practice Test

This sentence is about choosing a word that means three times as much or as big. The natural descriptor for a quantity that has increased by a factor of three is threefold. It fits both as an adjective and as an adverb, so you can say a threefold increase or the population grew threefold. It sounds formal and precise, which is why it’s the best fit for describing magnitude.

The other options aren’t as suitable for this meaning. Triple can convey the idea of three times, but it’s more common in fixed phrases or when naming things that come in threes, and it often carries a slightly different nuance. Tripled is a verb form, not an adjective describing a quantity. Tri-fold typically refers to something with three folds or panels, like a brochure, and doesn’t express a multiplier.