Practice adding multi-digit numbers using the standard algorithm. A geographical fact related to the answer will be revealed once each problem is correctly solved
A. Add two 4-digit numbers with and without regrouping in one place using a disk model
B. Add two 4-digit numbers with and without regrouping in two places using column addition and a disk model
C. Add two 4-digit numbers with and without regrouping in one place using a disk model part II
D. Add multi-digit numbers with regrouping in multiple places using column addition and disk models
E. Add multi-digit numbers with regrouping in multiple places using column addition