Exams

At least one black can be chosen in two ways from each box:
Now, probability of choosing at least one black ball from first box 

= 1/2 × [ (2C1× 2C1)/4C2 + 2C2/ 4C2 ]= 5/12

Probability of choosing at least one black ball from 2nd box
= 1/2 × [(4C1×12C1)/16C2 + 4C2/ 16C2] = 9/40

Final probability

= 5/12 + 9/40 = (50 + 27)/120 = 77/120

E=(1+i/n)^n-1

The Debit balance recovery is usually made by raising a credit memo for the regular vendors. However if there are no future transactions from the supplier, we ask the vendor to send the check / make an EFT for the amount due from him. When payment is made to the wrong vendor or payment made in excess, in that case overpayment has gone to the vendor, so for us it is vendor debit balance. For debit balance recovery, we can either follow- up with the vendor to send us the excess amount / refund back, or we can adjust that extra amount in future invoices submitted by that vendor. In case no future transactions, we have to follow-up with the vendor, failing which we have to write off this amount. 

Total cost = deposit + loan + interest
= 1231.67 + 2463.33 + 237.55
= $3932.55