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📏 Addition and Subtraction Practice

Add tens to three-digit numbers in your head, crack missing-number puzzles like 245 + ? = 380, and show sums as jumps along a number line.

lessons

~30 min

to learn

🔢 Math

subject

Ages 6–12

level

Start the course →

What you’ll learn

Adding Tens in Your HeadMentally add and subtract whole tens to and from three-digit numbers.Adding or subtracting whole tens changes only the tens digit; the hundreds and ones stay put. 345 + 40 = 385 and 462 − 30 = 432. Trust that the ones never move and these become quick mental jumps.
Missing-Number PuzzlesSolve missing-number problems by using the opposite operation and checking the result.When a number is missing, use the opposite operation to find it: 245 + ? = 380 means 380 − 245 = 135. The unknown can sit in any position, so choose add or subtract to uncover it, then check by substituting your answer back.
Sums on a Number LineRepresent numbers and sums on a number line as evenly spaced points and jumps.A number line places whole numbers at equal steps, like a ruler. Sums become jumps: 38 + 27 hops 2 to 40 then 25 to 65. Hopping to a friendly round number first makes the moves easy and shows exactly how numbers grow.

Questions this course answers

What is 345 + 40?

Add 4 tens to the 4 tens already there; hundreds and ones stay: 385.

What is 462 − 30?

Take 3 tens from 6 tens to leave 3 tens; hundreds and ones stay: 432.

What is the missing number in 245 + ? = 380?

Subtract to undo the addition: 380 − 245 = 135.

To find ? in 500 − ? = 350, what should you do?

500 − 350 = 150 gives the missing amount that was taken away.

Why is checking a missing-number answer a good idea?

Substituting your answer back confirms the equation balances.

On a number line, the marks are...

A number line has equally spaced points, each one step apart.

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.

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