eBank

[MBA.Aspirant]

An online bank verifies customers' ownership of external bank accounts by making both a small deposit and a small debit from each customer's external account, and asking the customer to verify the amounts. In 70% of these exchanges, the deposit and debit are within two cents of one another (for example, a deposit of $0.18 and a debit of $0.16, or a deposit of $0.37 and a debit of $0.38), and the deposit and debit are always within five cents of one another. During one week, the online bank attempts to verify 6,000 accounts in this manner, but 0.5% of the transactions do not go through, and thus no money is transferred. What is the maximum amount, in dollars, that the account verification system could have cost the bank that week?

(A) $165.30
(B) $173.40
(C) $174
(D) $256.71
(E) $258

[user123321]

An online bank verifies customers' ownership of external bank accounts by making both a small deposit and a small debit from each customer's external account, and asking the customer to verify the amounts. In 70% of these exchanges, the deposit and debit are within two cents of one another (for example, a deposit of $0.18 and a debit of $0.16, or a deposit of $0.37 and a debit of $0.38), and the deposit and debit are always within five cents of one another. During one week, the online bank attempts to verify 6,000 accounts in this manner, but 0.5% of the transactions do not go through, and thus no money is transferred. What is the maximum amount, in dollars, that the account verification system could have cost the bank that week?

(A) $165.30
(B) $173.40
(C) $174
(D) $256.71
(E) $258

is it B?

user123321

[neelgandham]

Number of attempts to verify accounts = 6000
Successful attempts to verify accounts = 6000-30 = 5970
To maximize the cost let the difference between the deposit and debit of 70% of the accounts be 0.02 and the rest 30% be 0.05.
Total cost to the bank = $5970*0.7*0.02+5970*0.3*0.05 = $5.970(14+15) = $29*5.97 = $173.13 ~ $173.40

IMO B