Four subtract 1.15 equals what?
We could use the inverse operation to help us find the answer. What do we need to add to 1.15 to give us four? So if we start at 1.15, what do we need to add to take us to the next whole number, which is two? 0.85. How do we get from two to four on the number line? We just need to add two. Two and 0.85 is 2.85. Four subtract 1.15 equals 2.85.
We calculated our answer using the inverse operation, or in other words, finding out what we needed to add to 1.15 to get us to four. 1.15 plus 2.85 equals four, which means that four take away 1.15 equals 2.85.