These are the orders that arrived on the floor of the BATs exchange last week.

Time	Trader	Buy/sell	Visibility	Price	Size
9:30	Cathy	Sell		50.12	1,000
9:30	David	Buy		50.05	1,000
9:30	Gina	sell	hidden	50.10	200
9:31	Amy	Sell		50.10	400
9:31	Fred	buy		50.03	400
9:32	Bill	sell		50.11	500
9:32	Ellen	Buy		50.04	500

1) At 9.40 Bob submits an order buy 200, limit 50.10. Explain whether a trade will occur, and if so, who are the counterparties? What is the price and size of each counterpartys trade?

2) If instead, Bobs order had been sell 1200, limit 50.04. Explain whether a trade will occur, and if so, who are the counterparties? What is the price and size of each counterpartys trade?

3) To the original book, Bob submits Buy 500, limit 50.11. Explain whether a trade will occur, and if so, who are the counterparties? What is the price and size of each counterpartys trade?

4) What does the limit order book look like after the order in question (3) above?