3-digit number plus multiple of 10
for 2nd grade

Mental calculations: 3 digit numbers plus tens

Learn how to add multiples of ten to 3 digit numbers

When we want to add a smaller number to a bigger number, there are sometimes shortcuts that make it easier. If the smaller number is 10 or a multiple of 10, adding that number to a bigger number just means increasing the tens column of the bigger number by the number of tens you are adding.

So, for instance, if you want to add:

248 + 30

all you need to do is add 3 to the tens column value which is 4, so you get 7 for the tens column. The rest of the big number stays the same, so the total addition looks like this:

248 + 30 = 278

In the same way, adding 419 and 70 gives:

419 + 70 = 489

It is the same idea if you want to add hundreds to 3 digit numbers but this time you would add to the hundreds column value by the number of hundreds you want to add. Adding units is often just going to affect the units column, so for instance, 271 + 5 = 276 because all we had to do was add 5 to the units column value to get an answer.