Subtracting Across Zeros: Rainbow Castle

Welcome to Rainbow Castle! Princess Ruby is getting ready for a royal ball, with rose bushes, heart balloons and crowns on velvet cushions. Big round numbers like 400 have zeros, and taking away from a zero needs a clever trade.

Remember: 400 − 167: no ones and no tens to borrow, so trade 1 hundred for 10 tens, then 1 ten for 10 ones. 400 becomes 3 hundreds, 9 tens and 10 ones. 10 − 7 = 3, 9 − 6 = 3, 3 − 1 = 2, so 233.

Magic trick: Take 1 from both numbers first! 400 − 167 is the same as 399 − 166, and that needs no borrowing at all: 233.