Level 1 · Ages 6–8
Read it again any time, including while you work through the exercises.
Three children compare their card collections: 56, 65 and 506 cards. Who has the most? To find out, you need to order the numbers. Good news: you already own the magic tool, hundreds, tens and ones!
To compare two numbers, first look at who has more digits: 506 has three digits, so it beats the two digit numbers. If they have the same number of digits, compare from left to right: first the hundreds, then the tens, then the ones. So 65 beats 56 because 6 tens is more than 5 tens.
Sandwiching a number means trapping it between two round numbers, like in a sandwich: 47 is trapped between 40 and 50. We write 40 < 47 < 50. The symbol < means "is smaller than": the point always aims at the smaller number.
And rounding? It means choosing the closest round number. 47 is closer to 50 than to 40, so 47 rounds to 50. It is very handy in real life: if a toy costs 47 coins, you know you need about 50 coins. Golden rule: look at the digit just to the right, if it is 5 or more, go up, otherwise stay.
In this lesson, you will become a champion of ordering, sandwiching and rounding. Let's go!
Order from smallest to largest: 340, 304, 430.
340 -> 3.., 304 -> 3.., 430 -> 4..
I compare the hundreds first: 340 and 304 have 3 hundreds, 430 has 4. So 430 is the largest.
340 -> 4 dizaines, 304 -> 0 dizaine
To split 340 and 304, I move to the tens: 4 tens versus 0 tens. So 304 is smaller than 340.
304 < 340 < 430
Now I can order everything from smallest to largest.
Result: 304 < 340 < 430
Round 276 to the nearest ten.
270 < 276 < 280
First I sandwich 276 between two tens: it is trapped between 270 and 280.
chiffre des unités : 6
I look at the ones digit: it is 6, and 6 is 5 or more, so I go up.
276 ≈ 280
276 is closer to 280 than to 270: the rounding to the nearest ten is 280.
Result: 276 rounded to the nearest ten is 280.