1) This document discusses different methods for estimating sums, differences, and quotients of numbers, including rounding, front-end estimating, and clustering. 2) Rounding involves rounding decimal numbers to place values like tenths or hundredths to make calculations easier. Front-end estimating adds the digits before the decimal and estimates the digits after separately. 3) Clustering works by finding a cluster value that a group of numbers centers around, like phone bills centering around $15, and using that value to estimate totals.