This document discusses concepts in social arithmetic including buying and selling, profit and loss calculations, savings accounts, and loans. It provides formulas for calculating profit percentage, loss percentage, interest earned on savings, and monthly loan payments. Examples are given for calculating the profit percentage earned by a motorcycle dealer, determining the sale price of durians after some spoiled and resulted in a 7% loss, calculating the balance of a savings account earning 8% interest after 9 months, and finding the monthly payment for a 10-month loan with 12% annual interest.