In the first part of the lesson, we use base-ten blocks. A THOUSAND blocks make a cube. One HUNDRED is a "flat", a TEN is a "stick", and one little block is a UNIT or ONE. We see several numbers with four digits made with these blocks, and write them as numerals.
In the second and short part, we write "seven thousand seventy" as a number, and then place four-digit numbers on a number line.
In the final portion of the lesson, we write several four-digit numbers in expanded form: as a sum of the different "parts" according to place value. Then we also fill in the missing parts from the expanded form. For example, the number 3,405 is written as a sum: 3000 + 400 + 0 + 5.
Add and subtract 4-digit numbers — a lesson on estimation
Math Mammoth Grade 3 curriculum