Mental Math · Foundations · F1
Every number is built from place values — hundreds, tens, and ones. Once you can split a number into its parts and put it back together, mental math becomes easy. We read and work from the big parts first, the way your brain naturally wants to.
Take it apart
Tap the number to break it into place values.
Watch the method
A number is just its place values added together. Splitting it apart — and rebuilding it — is the move every mental method is built on.
3 in the hundreds place is worth 300.
4 in the tens place is worth 40.
7 in the ones place is worth 7.
Put the parts back together and you have the number.
The number 347 secretly means 300 + 40 + 7. The same digit means different amounts depending on where it sits: the 3 is worth 300, not 3.
Why it works
Think of coins: hundreds, tens, and ones. 347 is three $100 bills, four $10 bills, and seven $1 coins.
On paper we add starting from the ones (right to left). In your head it is easier to start from the biggest part (left to right), because you get a rough answer immediately and refine it.
Why it works
If someone asks for 347 + 200, you instantly think 547 — you started from the hundreds.
What is 50 + 8?
Read the parts
50 is five tens, 8 is eight ones.
Join them
Five tens and eight ones is the number 58.
Break 347 into place values.
Hundreds
The 3 is in the hundreds place → 300.
Tens
The 4 is in the tens place → 40.
Ones
The 7 is in the ones place → 7.
Write it
347 = 300 + 40 + 7.
What number is 1000 + 200 + 30 + 4?
Stack the places
One thousand, two hundreds, three tens, four ones.
Read it off
That is 1234.
The 4 in 347 is worth 4.
Its place decides its value. In 347 the 4 sits in the tens place, so it is worth 40.
You must always start from the ones, like on paper.
That is just the paper algorithm. In your head, starting from the biggest place is faster and gives an instant estimate.
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