Subtract Across Zeros - Arithmetic Step by Step

Subtract 157 from 400. Both the ones and tens digits are 0, so borrowing must chain: first borrow from hundreds into tens, then from tens into ones.

Example

sub-400-157.math

   400
-  157
------

step: ones: 0 < 7, need to borrow; tens is 0
step: borrow from hundreds: 4 -> 3, tens 0 -> 10
step: borrow from tens: tens 10 -> 9, ones 0 -> 10
step: ones: 10 - 7 = 3, write 3
step: tens: 9 - 5 = 4, write 4
step: hundreds: 3 - 1 = 2, write 2
step: 400 - 157 = 243

borrow-across-zeros When the tens digit is 0, you cannot borrow directly into the ones column. First borrow from the hundreds: hundreds decreases by 1 and tens becomes 10. Then borrow from tens into ones: tens decreases by 1 (to 9) and ones increases by 10.