Last winter Armand had Start Fraction 5 Over 6 End Fraction of a row of stacked logs. At the end of the winter he had Start Fraction 8 Over 15 End Fraction of the same row left. How much wood did he burn over the winter?

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?