Addition and subtraction with 4-digit numbers - mental math
Here are some fairly easy mental addition & subtraction problems with 4-digit numbers. Many of them are based on just thinking in "whole hundreds", such as 2900 + 600 is like 29 + 6 (hundreds).
Next, we solve various addition/subtraction word problems with 4-digit numbers, using mental math only. :) In the last one, Mathy goes jogging in the woods, and we're given distances of the different legs of the jogging track, but there is no question! So, once again, we need to make a question. :)
See also
A lesson on estimation — add/subtract 4-digit numbers
Math Mammoth Grade 3 curriculum