Counting on and back

In your book, Maths Mela (Chapter 4), you count on and count back with 4-digit numbers. Counting on from 1027: 1028, 1029, 1030, 1031. Look at what happens after 1029: the 9 ones and 1 more make a ten, so the tens digit goes up and the ones go back to 0.

Counting back from 4892, the numbers before it are 4891, 4890, 4889. And counting back from 8002: 8001, 8000, 7999. The number just before 8000 is 7999.

The book has a place-value slider, with a strip for each place. To increase a number by 1, move the ones up by 1: 1895 + 1 = 1896. To increase by 10, move the tens up by 1: 2785 + 10 = 2795. To decrease by 2, move the ones down by 2: 3369 − 2 = 3367. To decrease by 10, move the tens down by 1: 5648 − 10 = 5638.

Take care when a place goes past 9. 6487 + 20: the tens go 8, then 9, then one more makes 10 tens, which is 1 hundred. So the hundreds go up from 4 to 5 and the tens become 0: 6487 + 20 = 6507.