供需破題 （二）
翁sir親口解
上期提到現象／phenomenon一詞，由於經濟科內，在供需課題中有「現象」的題目只有「短缺(Shortage)」與「盈餘(Surplus)」兩種，本期翁Sir將會把題目要求的難度加深，探討當現有現象／phenomenon時，若價格不變(Price remains unchanged)，需求(Demand)或供應(Supply)改變時的情況。
例子一：在繁忙時間，香港海底隧道(即紅隧)(收費為$20)，出現有交通擠塞。假設西隧由$75調高收費至$80，但紅隧的收費卻沒有調整。試以一圖輔助，解釋為何在上述情況下，紅隧在繁忙時間會變得更為擠塞。 (6分)
Example 1：The traffic using the Cross Harbour Tunnel (俗稱紅隧)(fee : $20) is congested during the rush hours. Assume the tolls of the Western Harbour Crossing increased from $75 to $80, the tolls of the Cross Harbour Tunnel remained unchanged. With the aid of a diagram, explain why in this situation, the traffic using the Cross Harbour Tunnel during the rush hours would become more congested. (6 marks)
拆題拆字：由於題目指出現有「交通擠塞」／congested，代表現有短缺／Shortage的現象。當題目指出紅隧的替代品(Substitutes)西隧加價，其需求量(Quantity demanded)下降，紅隧的需求(Demand)上升。同學要留意，題目明確指出紅隧的收費卻沒有調整／Cross Harbour Tunnel remained unchanged，即其價格不變！
文字解說︰紅隧是西隧的代替品，當西隧加價，其需求量下降，紅隧的需求增加。在收費不變下，隧的超額需求增加，更擠塞。
Explanation: Cross Harbour Tunnel is a substitute of Western Harbour Tunnel. When Western HarbourTunnel increase it’s fare, the quantity demanded decrease, – demand for Cross Harbour Tunnel service increases , with a fixed price, excess demand for the Cross Harbour Tunnel service would increase
例子二：在2020年，新冠肺炎對香港的經濟有重大影響。在新冠肺炎爆發初期，航空公司沒有減票價，也沒有減少班次。結果，飛往香港的航機都有大量的空置機位。 以圖輔助，解釋上述經濟現象，並解釋這些航空公司的總收入如何受影響。 (8分)
Example 2：At the outbreak of COVID-19, airlines did not reduce air fares or the number of flight. As a result, there were a lot of empty seats on planes flying to Hong Kong. With the aid of a diagram, explain the above economic phenomenon, and explain how the total revenue of these airlines was affected. (8 marks)
文字解說︰當新冠肺炎爆發，航空服務的需求減少，在固定機票價格下的交易量減少，出現盈餘，總收入減少。
Explanation: Outbreak of COVID-19, a decrease in demand for airline services, quantity transacted decreased at the constant price, there is surplus and total revenue decreased.
同學亦可假設市場原先有超額供應或超額需求，上述分析仍然適用
翁 Sir 信箱
同學若有任何經濟科的問題，歡迎電郵翁 sir : [email protected]
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