(i) Invoice is a business document or bill or statement giving the details of goods sold as to the quantity, quality, price, total value, etc.
(ii) Thus the invoice is a source document of prime entry both for the buyer and seller. It is purchase invoice or inward invoice for the buyer and sales invoice or outward invoice for a seller

(i) At the end of the accounting year, all nominal accounts are closed but the business has to be carried on with previous year's assets and liabilities.
(ii) Journal entry made in the beginning of the current year with the balances of assets and liabilities of the previous year is opening journal entry.

According to the Negotiable Instruments Act, 1881, "Bill of exchange is an instrument in writing containing an unconditional order, signed by the maker, directing a certain person to pay a certain sum of money only to, or to the order of a certain person or to the bearer of the instrument".

(a) Endorsement of a bill :
(i) Endorsement means signing on the face or back of a bill for the purpose of transferring the title of the bill to another person. The person who endorses is called the "Endorser".
(ii) The person to whom a bill is endorsed is called the "Endorsee". The Endorsee is entitled to collect the money.
(b) Discounting of a bill :
(i) When the holder of a bill is in need of money before the due date of a bill, he can convert it into cash by discounting the bill with his banker. This process is referred to as the discounting of bill.
(i) The banker deducts a small amount of the bill which is called discount and pays the balance in cash immediately to the holder of the-bill.

The advantages of maintaining subsidiary books can be summarised as under :
(i) Proper and systematic record of the business transactions : All the business transactions are classified and grouped conveniently as cash and non cash transactions, which are further classified as credit purchases, credit sales and returns etc.
(ii) Convenient posting: All the transactions of a particular nature are recorded at one place, i.e., in one of the subsidiary books. For Example: All credit purchases of goods are recorded in the purchases book and all credit sales of goods are recorded in the sales book.
(iii) Division of work: As journals are sub-divided, the work will be sub-divided and different persons can work on different books at the same time and the work can be speedily completed.
(iv) Efficiency: The sub-division of work gives the advantage of specialisation. Thus specialisation leads to efficiency in accounting work.
(v) Helpful in decision making: Subsidiary books provide complete details about every type of transactions separately. Hence the management can use the information as the basis for deciding its future actions.
(vi) Prevents errors and frauds: Internal check becomes more effective as the work can be divided in such a manner that the work of one person is automatically checked by another person. With the use of internal check, the possibility of occurrence of errors or fraud may be avoided or minimised.
(vii) Availability of requisite information at a glance : The maintenance of subsidiary books helps in obtaining the necessary information at a glance.

Note: Sold goods to Shyam for cash on Dec. 26, 2017 will not be recorded in the sales book, because it is cash sales.

29^th may 2017 transaction is purchase of an asset. Hence the transaction will not be recorded in the purchases book.