3.NBT.A.2

Fluently add and subtract within 1000 using strategies and algorithms based on place value, properties of operations, and/or the relationship between addition and subtraction.

Add and subtract within 1000 using the standard algorithms (carry and borrow). Do not rely on manipulatives or drawings. Conclude by giving your students this challenge.

Note: The MAA associates this problem with 7.SP.C.8.b, but this problem has nothing to do with probability, it's just straight logical deduction.