1. "Only three meters separate the runners in first and second place." - Perfectly natural and clear. 2. "Three hours seems like a long time to spend on homework." - Completely natural, especially in casual speech. 3. "It seems like a long time to spend on homework." - Also natural and slightly more general than the previous sentence. 4. "Around 40% of the electorate decides their vote on election day." - Sounds fine, though some might say "make up their minds" instead of "decides their vote" in very conversational English. 5. "More than half of the adult population in Peru is overweight." - Flows naturally. No changes needed. 6. "A large part of the population prefers to exercise more rather than eat more healthily." - Natural, but you could tweak it slightly to make it smoother: "A large part of the population prefers exercising to eating healthier." 7. "Around a third of the country’s population lives in the capital city." - Perfectly natural. 8. "On average, 25 liters of water are used each day to fill the pool, which in my opinion is a waste of resources." - Very natural and precise. 9. "3 centimeters was all that separated the first two runners in last night's race, so the sports club declared it a dead heat." - Natural, though for better flow, you could say: "Only three centimeters separated the first two runners in last night's race, so the sports club declared it a dead heat." 10. "I like the band, but I’ve never been to any of their concerts." - Perfectly fine and casual. When aiming for natural English, keep sentences concise, use contractions (e.g., "I’ve" instead of "I have"), and opt for simpler phrases where possible—native speakers often prioritize ease over formality in everyday speech!

Your sentences are mostly natural, but here are a few small adjustments to make them sound even more fluid in everyday spoken English: 1. Only three meters separate the runners in first and second place.
This sounds natural. 2. Three hours seems like a long time to spend on homework.
Perfect, sounds natural. 3. It seems like a long time to spend on homework.
This is fine, but you could add "three hours" to clarify, like: "Three hours seems like a long time to spend on homework." 4. Around 40% of the electorate decides their vote on election day.
This sounds fine, but "decide" might flow better than "decides." So: "Around 40% of the electorate decide their vote on election day." 5. More than half of the adult population in Peru is overweight.
This is natural. 6. A large part of the population prefers to exercise more rather than eat more healthily.
A slight tweak: "A large part of the population prefers exercising more rather than eating more healthily." 7. Around a third of the country’s population lives in the capital city.
This sounds great. 8. On average, 25 liters of water are used each day to fill the pool, which in my opinion is a waste of resources.
This is natural. 9. 3 centimeters was all that separated the first two runners in last night's race, so the sports club declared it a dead heat.
It sounds good, but "3 centimeters were all that separated..." might sound slightly more natural with plural agreement. 10. I like the band, but I’ve never been to any of their concerts.
This is natural! Your sentences are really close to perfect already!

Saludos Gerardo. Yes, the grammar is fine on each of these sentences. All of these sound as if they come from a news article or documentary style of speech/writing. I only say that because you asked if it is used in "everyday speech". Ill use two examples: - "on average, 25 liters of water are used ....waste of resources" - more commonly it would be said like this: "yeah, it takes a lot of water, like 25 liters to fill it up. a waste, really" - "I like the band ...concerts" -- this one does actually sound like it is used in common everyday speech

The sentences are all good. Most of the sentences use a singular or plural in situations where either is acceptable. For example, you can say "three hours seems" or "three hours seem". Likewise, you can say "40% of the electorate decides", or you can use "decide". The meaning is the same in each case, but it matters which one you choose because it tells something about how you are thinking. If you say "three hours seems", it means you think of those hours as a single unit, a single period of time. If you say "three hours seem", it means you are thinking about the hours individually. I prefer "seem" because it draws attention to the fact that you must endure all of those hours one by one: what torment!

All of these example sound great, good job!