Not to support google but it is a really bad use of AI, AI is meant to do research and find logical answers to them
So this is "normal" that an AI is bad in pure calculation, as it tries to find the most probable answer whereas math operations are not option A with 20% and option B with 80% but pure logical and linear thought
So in a way google (and others) are really dumb to let pure AI do the whole rather than to fetch and organize the work with proper tools (in this case should research the world population in 2015 and 2025 and start a calculation with a regular calculator like program)

AI is great (sometimes), but the overhype over it make it used in every domain rather than useful ones...