Answer
See explanation
Work Step by Step
1) T1 reads the balance of account
A → say it's $\$500$
2) T2 transfers $\$100$ from A to B:
A becomes $\$400$
B increases by $\$100$ (e.g., from $\$300$ to $\$400$)
3) T1 reads the balance of account B → now it's $\$400$
4) T1 computes the sum: $\$500 (A) + \$400 (B) = \$900$
This is incorrect because the actual total after T2's transfer should still be $\$800$ (assuming no other changes), because the transfer just moved money between accounts. But T1 used the old value of A and the new value of B, leading to an inflated sum of $\$900$.
