This Problem Set is a part of the Lesson 21, Unit 6, Grade 1. This lesson introduces the quarter, which can be the most challenging coin to learn. Students build on their understanding from the previous lesson, focusing specifically on the value of 25. Then they consider how many pennies they would need to have the same value as 1 quarter and then trade in, for example, 2 dimes and 1 nickel or 2 dimes and 5 pennies for a quarter.