Doubles Minus One and Other Near Doubles Shortcuts

Look for this idea outside of your lessons. Two roads to one answer is common in math. When both roads agree, you can trust your work. This is worth learning because having two paths means you can always check your own answer.

Watch for it today, and when you spot it, tell someone what you noticed and how you knew. Ask yourself where else the same idea might be hiding, then go and look. Let us think about this slowly. You can also go the other way.

For 7 plus 6, start with the double seven plus seven, which is fourteen, then take one away because six is one less than seven. The answer is thirteen. Notice that doubles plus one and doubles minus one give the same answer for the same problem, because you can build it from either neighbor. Choose whichever double you remember faster.

Try both ways on one problem and compare. For 8 plus 9, you can say eight plus eight plus one, or nine plus nine minus one. Both give seventeen. When two different roads reach the same place, that is strong evidence your answer is right. Show your work to someone and explain it in your own words.