Determine by truth tables whether he following logical arguments are valid, or fallacies: p→q, q→r ⊢ p→r

Find the value of the variable and the length of each secant segment.

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?

If the probability of an event happening is 65% then the probability this event does not occur?