What is 12.345 rounded to the nearest tenth

Rounding to the nearest tenth means rounding to the decimal place directly to the right of the decimal. 

The rules of rounding are fairly simple. If the number to the right of the number you are rounding is greater than or equal to 5, you round up. If the number to the right is less than 5, you round down.

Let's take a look at the number 12.345.
First, round to the hundredths place. The number right before the 4 is 5, so we round up. This gives us the number 12.35.
Next, we have to round to the tenths place. The number to the right of the 3 is 5, so we round up as well. This gives us the number 12.4.

12.4

The answer to your question 12.3 because it the number the the hundredth place is smaller the 5 you round down