Which is longer, 5 miles or 10 kilometers

Imagine a new pasture with grass growing on it. every day after the seeds have germinated, the number of blades of grass in the pasture triples. after 18 days, the entire pasture is completely covered in grass. how many days did it take for the pasture to be one-third covered in grass?

What number should be added to both sides of the equation to complete this square? x^2-10x=7

Ben is three times as old as samantha, who is two years older than half of michel's age. if michel is 12. how old is ben?