Subtract from right to left, one column at a time.
Problem 09
Column 1 of 2 · ones
Work from right to left ←
Push → to turn 1 into 10. Push ← to turn 10 back into 1.
One pip is one group in its column. The total stays the same.
tens
3 × 10
ones
6 × 1
tens
ones
3
6
11Start with the ones.
Use the arrows for each trade. Click an answer box to open its digit wheel.
Push between places to regroup. Choose a digit from its wheel; correct answers advance automatically.
9Solved today
2Perfect streak
Borrow through zeros one column at a time. Push left to undo a trade.