This strategy is wonderful because you can solve three digit addition problems in your head!

456
+521

Step 1: Add the values in the ones place. (Example: 6+1=7)
Step 2: Add the values in the tens place. (Example: 50+20=70)
Step 3: Add the values in the hundreds place. (Example: 400+500=900)
Step 4: Add the partial sums starting with the biggest number. (Example: 900+70+7) Less