How long will it take if you're going 45 miles per hour and you have 135 miles to go?

The? half-life of a radioactive substance is 20 years. if you start with some amount of this? substance, what fraction will remain in 120 ? years

Suppose that sahil knows that 45 people with ages of 18 to 29 voted. without using a calculator, he quickly says then 135 people with ages of 30to 49 voted. is he correct? how might sohil have come up with his answer so quickly?

Iknow its nothing to do with education, but what type of thing should i wrote here? ? : ) its for mcdonald's btw.