Finding Missing Numbers in Subtraction Sentences

You will meet this idea in ordinary days. A shopkeeper who knows what he started with and what remains can figure out exactly how much sold, without watching every sale. This is worth learning because knowing which piece is missing tells you whether to add or subtract. Watch for it today, and when you spot it, tell someone what you noticed and how you knew.

Here is today’s math treasure. Blanks appear in subtraction too. In 14 minus blank equals 9, ask what leaves fourteen and leaves nine behind. Count from nine up to fourteen: five steps. So five left.

Check it: fourteen minus five is nine. In blank minus 3 equals 7, you know what left and what stayed, so add them back: seven plus three is ten. Always ask which number is missing before you decide what to do.

Here is the key habit. Point at each number and name its job: this is the start, this is what left, this is what stayed. Once you know which job is missing, you know whether to add or subtract without any guessing at all. Take your time. Careful is better than fast.