Double Digit Addition - Practice & Answer Key - 40 questions / page * 5 pages = 200 questions. - 5 pages answer key with speed & accuracy guide. - All worksheets are printable pdf documents. - Great for students who are just learning how to add 2 digit numbers. *Some double-digit problems need regrouping! CCSS.Math.Content.2.NBT.B.5 Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.