I am having trouble with decimals. If i add 8+3+0.9+0.31=51 am i correct

No. You are not correct.

You only have two whole numbers. They add up to 11.

You have two numbers less than one.

. 0.90
+ 0.31
_______
= 1.21

11 + 1.21 = ?

Think of money.

8 dollars + 3 dollars + 90 cents + 31 cents.

the decimal places must be on the same line when adding.

so it should look like this
.9
.31
8.0
+3.0
______

i hope that helped..!

To check if your addition is correct, let's add the numbers step by step:

1. Add the whole numbers: 8 + 3 = 11.
2. Add the decimals: 0.9 + 0.31 = 1.21.

Finally, add the sum of the whole numbers to the sum of the decimals: 11 + 1.21 = 12.21.

Therefore, the correct answer is 12.21, not 51. It seems there may have been an error in your calculation.