Fraction Estimation & Reasonableness

How the lesson starts: Fraction Estimation & Reasonableness

Captain Zara's fuel
Captain Zara is flying her rocket. She has no time to measure fuel exactly. She just asks: is the tank near empty, half full, or full? Those friendly numbers, 0, 1/2 and 1, are called benchmarks!
Near 0, 1/2 or 1?
Here's a fuel gauge from 0 to 1. 1/9 sits right by 0: almost empty. 5/9 lands just past 1/2. 8/9 is nearly 1: almost full! Quick trick: compare the top with half of the bottom.
Estimate a sum
Zara pours 7/8 of a tank into one engine and 2/5 into another. 7/8 is almost 1. 2/5 is close to 1/2. So the total is about 1 1/2 tanks. And can 3/4 + 2/3 be 5/7? No! Both are more than 1/2, so the sum is more than 1.