1. Subtracting with Gerbert’s abacus

2. Subtracting on an abacus
9 1 7

3. Subtracting on an abacus
Start with the hundreds:
9 – 6 = 3

4. Subtracting on an abacus
Now go to the tens:
We have 1 – 4.

5. Subtracting on an abacus
Since 4 is larger
than 1, we go to the hundreds column and split the 3 into 2 and 1.

6. Subtracting on an abacus
Now we have
eleven tens, so we can subtract 4 from them to get 7 tens.

7. Subtracting on an abacus
Now we have
eleven tens, so we can subtract 4 from them to get 7 tens.

8. Subtracting on an abacus
Finally, we go to the ones column and subtract 2 from 7.

9. Subtracting on an abacus
The final answer is 275.