S4 ICT | Information Systems and E-commerce: Tutor Prep Guide (45-minute flow, script, common errors)

2026-11-15

Tutor lesson-prep guides · Secondary ICT

Students all say they shop online, yet ask whether the discount or the shipping comes first and seven in ten get it wrong. This lesson fixes a transaction as five ordered steps.

Objectives — By the end of the lesson students can: (1) distinguish B2B, B2C and C2C and give a Hong Kong example of each; (2) compute 480 dollars of goods at ten per cent off plus 30 dollars shipping as 462; (3) compute a 2.5 per cent gateway fee of 11.55 and a merchant receipt of 450.45; (4) get 6 days and 12 units left from 120 units selling 18 a day, and a reorder point of 108 from a four-day lead time and 36 units of safety stock; (5) get a conversion rate of 2 per cent from 4,000 visitors and 80 orders.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Percentages	What is 480 dollars at ten per cent off	432 dollars
Order of operations	Add 30 dollars shipping after the discount	462 dollars
Division with remainder	120 units selling 18 a day, how many days	6 days with 12 left
Ratios	80 orders over 4,000 visitors	2 per cent

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-6 min	Entry check	Ask the discount, the shipping step, 120 over 18 and 80 over 4000; keep answers on the right of the board	Spoken answers, working on paper
6-16 min	Act one: three trading relationships	B2B a book supplier to a school, B2C a shop to a shopper, C2C a second-hand marketplace; they differ in buyer, invoice and returns	Students give one example each
16-28 min	Act two: five steps from cart to settlement	Cart 480, discount 432, shipping 30, total 462, fee 11.55, merchant receives 450.45	Students write the five steps in order
28-38 min	Act three: stock and conversion	120 units at 18 a day gives 6 days and 12 left; reorder is 4 times 18 plus 36, so 108; 4,000 visitors and 80 orders is 2 per cent	Students compute the reorder point and the rate
38-43 min	Question types: total, fee, stock, conversion	The same chain with new numbers, four phrasings	Students do one and read out the unit
43-45 min	Exit check	Three spoken questions; note which act each error comes from	All three correct

03 Teaching script (read it out)

Scene 1: Act one: three relationships, differing in buyer and responsibility

E-commerce is not one thing but three relationships. B2B is company to company, such as a book supplier invoicing a school, where one invoice may run to six figures and returns follow a contract. B2C is a business to a consumer, which is ordinary online shopping with consumer protection and a return window. C2C is consumer to consumer, where a second-hand platform is only an intermediary: the goods belong to the seller and the return duty sits there too. One site can host all three, so when a question asks which type it is, ask first who buys and who sells.

A sale between two users on a second-hand platform is B2C or C2C, and who handles a return?

Scene 2: Act two: wrong order, wrong money

A transaction has a fixed order: goods amount, then discount, then shipping, then total, then the gateway fee. Three items total 480, ten per cent off leaves 432, and 30 dollars of shipping is added after the discount, giving 462. Reverse the order and 510 times 0.9 gives 459, so the customer underpays by three dollars, which the merchant absorbs. The gateway then charges 2.5 per cent of the whole transaction, so 462 times 0.025 is 11.55, and the merchant receives 450.45. Note the fee is charged on 462 rather than 432, because the shipping also passes through the gateway.

Should the fee be charged on 462 or on 432, and how much does the merchant gain or lose if you use 432?

Scene 3: Act three: stock is subtraction, the reorder point is addition

Stock of 120 units selling 18 a day: 18 times 6 is 108, so six full days leave 12 units. Write six days with 12 left, never 6.67 rounded to seven, because day seven has nothing to sell. Restocking begins with lead time: if the supplier takes four days, four times 18 is 72 units sold before delivery, and adding 36 units of safety stock gives a reorder point of 108, so place the order when stock falls to 108. Conversion comes last: 4,000 visitors and 80 orders is 80 divided by 4000, or 0.02, which is 2 per cent. Lifting that to 2.5 per cent gives 100 orders, twenty more for the same advertising spend.

If the supplier took six days instead of four, what happens to the reorder point, and why does it rise?

04 Question types and worked steps

Type	Example	Steps	Answer
Total payable	Goods 480 at ten per cent off, shipping 30	Discount first, shipping second, never reversed	432 plus 30, so 462 dollars
Gateway fee	The gateway charges 2.5 per cent of the total	Charge on 462, not on the discounted goods	11.55, leaving the merchant 450.45
Stock days	120 units selling 18 a day	Round the days down, then state the remainder	6 days with 12 units left
Reorder point	Four-day lead time, 18 a day, 36 safety stock	Lead days times daily sales, plus safety stock	108 units

Sanity check (teach this): Four checks: (1) a discount applies to the goods amount only unless the terms say shipping is discounted too; (2) the gateway fee applies to the whole transaction including shipping; (3) stock days round down and the remainder must be stated, never rounded up to seven; (4) a conversion rate is a decimal, so 2 per cent is 0.02, and an order count must come out above zero.

05 Independent practice (3 questions)

Question	Answer	What to watch
4,000 visitors and 80 orders: what is the conversion rate	2 per cent	80 divided by 4000 is 0.02
At 2.5 per cent on the same traffic, how many more orders	20 more, that is 100 orders	4000 times 0.025, then subtract 80
Goods of 250 at twenty per cent off plus 20 shipping: total	220 dollars	250 times 0.8 is 200, then add 20

06 Common mistakes and what to say

Mistake	Student writes	Say this
Adding shipping before the discount	Computing (480 plus 30) times 0.9 as 459	Unless the terms say otherwise the discount touches goods only. Your answer underpays by three dollars and the merchant loses it.
Charging the fee on goods alone	Using 432 times 0.025 to get 10.80	The gateway charges the whole transaction, shipping included. Only 462 gives 11.55, and 432 understates the fee by 0.75.
Rounding stock days up	Writing 6.67 days as seven days	Day seven has no stock. Round down, and state the 12 units left, or the reorder arrives late.
Treating C2C as B2C	Making the platform responsible for a marketplace seller returns	In C2C the platform is only an intermediary, so the seller owns the goods and the return duty. Ask who owns the goods first.

07 Homework (paper, section and question numbers)

S4 ICT Practice Paper 1, information systems and e-commerce — Section B, questions 5 to 8

08 Exit check (last 5 minutes)

Question	Answer	Decision
480 at ten per cent off plus 30 shipping: total	462 dollars	Wrong: reteach act two, discount before shipping
A 2.5 per cent fee on 462: what does the merchant receive	450.45 dollars	Wrong: reteach act two, the fee is on the total
120 units selling 18 a day: how long until sold out	6 days with 12 left	Wrong: reteach act three, round down and keep the remainder

09 Tutor FAQ

Which year level is this for?

Hong Kong S4 ICT uses e-commerce as a context for information systems, testing the order of a process and simple arithmetic. The S3 work on percentages and division is the prerequisite, so revise discounts and remainders first.

Is 45 minutes enough?

Yes, provided act two gets twelve minutes. The discount and shipping order is the likeliest error, so rather than adding a fifth question type, make sure students can recite the five steps.

Are these a real company figures?

No. 480 dollars, 2.5 per cent and 18 units are teaching numbers chosen for mental arithmetic. Real fees run from about 1.5 to 3.5 per cent; the method and the order matter, not one memorised rate.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.