Review: big numbers, adding and subtracting
Big numbers are read in periods of three digits: ones, thousands, millions and billions. The value of a digit depends on its place, and the number can be written in standard, word or expanded form. To compare, first compare the number of digits, then the digits from the left. To round, look at the digit to the right of the rounding place: 5 or more rounds up, 4 or less rounds down. Add and subtract place by place and regroup when needed, also across zeros. Check an addition by subtracting and a subtraction by adding. In a story, a bar model shows the parts and the whole. Estimate first so that a slip is easy to see.
| Digit | 4 | 5 | 0 | 7 | 3 | 2 | 0 |
|---|---|---|---|---|---|---|---|
| Place | millions | hundred thousands | ten thousands | thousands | hundreds | tens | ones |
| Value | 4,000,000 | 500,000 | 0 | 7,000 | 300 | 20 | 0 |
Number cards. Make a 7-digit number from seven cards. Read it aloud, write its expanded form and round it to the nearest million. Swap with a grown-up and check each other.