wunder beta

🧠 Adding and Subtracting in Your Head

Practice quick mental moves like 345 + 7 and 462 − 5. No paper needed — just place value and a little confidence.

lesson

~15 min

to learn

🔢 Math

subject

Ages 6–12

level

Start the course →

What you’ll learn

Numbers in Your HeadMentally add and subtract a one-digit number to and from a three-digit number, bridging a ten when needed.To add or subtract a few ones from a three-digit number, focus on the ones. 345 + 3 = 348 stays simple, but when the ones cross a ten you bridge: 345 + 7 hops to 350 then 352, and 462 − 5 dips to 460 then 457. Place-value thinking makes it a mental snap.

Questions this course answers

What is 345 + 7?

5 + 7 = 12, which adds a ten: 345 + 7 = 352.

What is 462 − 5?

2 − 5 won't go, so dip below the ten: 462 − 2 = 460, then 460 − 3 = 457.

When you add 345 + 7, why does the tens digit change?

5 + 7 = 12 makes a new ten, which bumps the tens digit from 4 to 5.

What is 345 + 3?

The ones don't cross a ten: 5 + 3 = 8, so 345 + 3 = 348.

What's the smart first move for 462 − 5?

Dipping to the round ten 460 first makes the rest of the subtraction easy.

Grounded in trusted sources

Khan Academy Kids
PBS Kids — early math
NAEYC — early math learning
Britannica Kids

Every Wunder lesson is built from real, reputable sources — never invented.

Related Math courses

🔢Adding and Subtracting Large Numbers 🔢Adding and Subtracting Two-Digit Numbers ➕Adding and Subtracting Within 100 🔄Adding in Any Order ⚡Addition and Subtraction Facts to 20 📏Addition and Subtraction Practice 🔢Addition and Subtraction Within 1,000 🔍Checking Answers by Rounding

Wunder is a personalized learn-anything platform — tell it any topic and it builds a beautiful, fact-checked course in minutes, with narration, a knowledge check, and a college-style University track.

Browse more Math courses · All topics · Home