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.

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.

Watch these Khan Academy videos:

- Missing number for 3-digit addition within 1000
- Worked example: Subtracting 3-digit numbers (regrouping)
- Worked example: Subtracting 3-digit numbers (regrouping twice)
- Worked example: Subtracting 3-digit numbers (regrouping from 0)
- Subtracting 3-digit numbers (regrouping)
- Adding 3-digit numbers
- Using place value to add 3-digit numbers: part 1

Do these Khan Academy exercises:

Next, give your students this challenge:

The Set of Numbers by NRICH

Conclude by leading this investigation:

Recamán’s Sequence

by MathPickle

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.