Learning Objectives
- 01
Add 2- and 3-digit numbers without writing anything down.
Left-to-Right Addition
Adding 2- and 3-digit numbers from the highest place value.
Topics
2-digit addition3-digit addition
Worked Examples
314 + 159=473
Break the second addend into place-value chunks (hundreds, tens, units) and add them one at a time so you only ever track one running total.
- 01
314 + 100 + 50 + 9
Apply this piece of the shortcut — running total 314.
- →
= 473
766 + 489=1255
Break the second addend into place-value chunks (hundreds, tens, units) and add them one at a time so you only ever track one running total.
- 01
766 + 400 + 80 + 9
Apply this piece of the shortcut — running total 766.
- →
= 1255
822 + 238=1060
Break the second addend into place-value chunks (hundreds, tens, units) and add them one at a time so you only ever track one running total.
- 01
822 + 200 = 1022; 1022 + 30 = 1052; 1052 + 8 = 1060
Start with the biggest piece — the hundreds (200). Big jumps first! 822 + 200 = 1060 — running total 1060.
- →
= 1060
Benjamin, Secrets of Mental Math — left-to-right addition
257 + 386=643
Break the second addend into place-value chunks (hundreds, tens, units) and add them one at a time so you only ever track one running total.
- 01
257 + 300 = 557; 557 + 80 = 637; 637 + 6 = 643
Start with the biggest piece — the hundreds (300). Big jumps first! 257 + 300 = 643 — running total 643.
- →
= 643
Benjamin, Secrets of Mental Math — left-to-right addition
834 + 381=1215
Break the second addend into place-value chunks (hundreds, tens, units) and add them one at a time so you only ever track one running total.
- 01
834 + 300 = 1134; 1134 + 80 = 1214; 1214 + 1 = 1215
Start with the biggest piece — the hundreds (300). Big jumps first! 834 + 300 = 1215 — running total 1215.
- →
= 1215
Benjamin, Secrets of Mental Math — left-to-right addition
Talking Points
- •Always work left-to-right — magnitude stays anchored.
Week 2 · Addition & Subtraction Mastery
Add and subtract rapidly using complements and compensation.
- →Add 2- and 3-digit numbers rapidly
- →Subtract efficiently without borrowing
- →Use complements to 100 and 1000
Sample Problems · Week 2
One simple and one intermediate problem to preview the week.
Simple · Day 3
74 − 29=45
Intermediate · Day 5
Change from $100 for $42.18=$57.82