Answer:
419
Step-by-step explanation:
Regrouping in subtraction: If we borrow from one group (tens group) and give to another (Once group) so that the operation can be completed, then this process is called regroup.
For example: We need to find the value of 52-39
We can not subtract 9 from 2. So we will borrow 10 from 50 and give to 2.
Now,
We need to find the greatest 3 digit number that can subtract from 426 so that we need to regroup.
To use regroup, the once digit must be more that 6. So, maximum value for once place is 9.
Therefore, the greatest 3 digit number that can subtract from 426 by using regroup is 419.