The idea
A digit’s position tells us its value. One hundred is ten tens, and one ten is ten ones. In a three-digit number, the places from left to right are hundreds, tens and ones. A zero keeps a place when there are none of that unit.
Before you begin: Count in ones and tens, and recognise two-digit numbers.
Write 342 as hundreds, tens and ones. Then exchange one hundred for tens.
Read the place of each digit. The 3 means three hundreds, the 4 means four tens and the 2 means two ones.
One hundred has the same value as ten tens. Exchanging it changes the groups, not the total.
Two hundreds remain. Add the ten new tens to the four tens already there.
A mistake to avoid
The digit 4 in 342 is worth 40, not 4. When regrouping, keep the total value the same.
Your turn.
Write this number in expanded form. What does its zero tell you?
Show the solution
There are five hundreds, no tens and seven ones. The zero holds the tens place.