Mathematics - Addition and Subtraction - Two-digit subtraction with regrouping - Not Enough Ones!

Show 42-17 visually: 4 ten-rods and 2 unit-cubes. 'We need to take away 7 cubes, but we only have 2! What should we do?' Options: A) Give up, B) Break apart a ten-rod into cubes, C) Take away 2 cubes only, D) Add more cubes from nowhere. The answer is B: borrowing/regrouping. Show the animation of a