Task
Find the difference:
| \(\displaystyle -\) | \(\displaystyle 1\) | \(\displaystyle 7\) |
| \(\displaystyle 8\) | ||
Solution
Step One.
From the ones of the number \(\displaystyle 17\) (this the digit \(\displaystyle 7\)) subtract the onese of the number \(\displaystyle 8\) (this is the digit \(\displaystyle 8\)):
\(\displaystyle 7-8{\small . }\)
But \(\displaystyle 7\) is less than \(\displaystyle 8,\) so we borrow one ten from the number \(\displaystyle 17\) and subtract:
\(\displaystyle 10+7-8=17-8=9{\small . }\)
| -1 | ||
| \(\displaystyle -\) | \(\displaystyle 1\) | \(\displaystyle \color{red}{7}\) |
| \(\displaystyle \color{red}{8}\) | ||
| \(\displaystyle ?\) | \(\displaystyle \color{red}{9}\) |
Step Two.
From the tens of the number \(\displaystyle 17\) (this the digit \(\displaystyle 1\)) we subtract one ten that we borrowed in the previous step:
\(\displaystyle 1-1=0{\small . }\)
| \(\displaystyle -\) | \(\displaystyle 1\) | \(\displaystyle 7\) |
| \(\displaystyle 8\) | ||
| \(\displaystyle \color{red}{0}\) | \(\displaystyle 9\) |
Answer: \(\displaystyle 9{\small . }\)