What is $2.43-1.2$?
To subtract two decimals, I need to line up the decimal points and subtract column by column, starting from the rightmost digit and borrowing if necessary. I can write $2.43-1.2$ as $2.43-1.20$ to make the columns align better. Now I can subtract the hundredths: $3-0=3$. Then I subtract the tenths: $4-2=2$. Finally, I subtract the ones: $2-1=1$. I bring down the decimal point and I get the answer: $1.23$. 