The Cost of a School Fundraiser Stall
A Year 8 class runs a smoothie stall at the school fete. They buy 12 kg of frozen mango at $9.50 per kilogram, 6 litres of yoghurt at $4.20 per litre, and 200 paper cups at $0.08 each. They plan to sell each smoothie for $4.00 and predict they will sell 180 cups, using about 150 g of mango and 60 mL of yoghurt per cup. On the day, they actually sell only 140 cups and throw away all the leftover mango and yoghurt because it cannot be reused. Two students also spent $18 on a banner from the class budget. The teacher asks the group to work out whether the stall made a profit and to explain what went wrong with their planning.
1. Calculate the actual profit or loss of the stall. Show each cost and the revenue.
Read the worked answer
Revenue: 140 cups × $4.00 = $560.
Costs:
- Mango: 12 kg × $9.50 = $114.00 (all bought, all counted as spent)
- Yoghurt: 6 L × $4.20 = $25.20
- Cups: 200 × $0.08 = $16.00 (bought 200, used 140, but the rest are a sunk cost)
- Banner: $18.00
Total cost = $114.00 + $25.20 + $16.00 + $18.00 = $173.20.
Profit = $560 − $173.20 = $386.80.
The key judgement is that leftover ingredients were thrown away, so their full purchase cost still counts. A student who counts only the mango and yoghurt used (about 21 kg of mango used is impossible, so check: 140 × 150 g = 21 kg, more than 12 kg bought - this shows the prediction was inconsistent) will get a different answer. The correct reasoning is to use the actual amount bought, not the amount used.
2. The group predicted they would use 150 g of mango per cup for 180 cups. Did they buy enough mango? What does this tell you about their planning?
Read the worked answer
Predicted mango needed = 180 cups × 150 g = 27 000 g = 27 kg.
They bought only 12 kg, which is less than half of what they predicted they needed. So even if they had sold all 180 cups, they would have run out of mango after 12 000 ÷ 150 = 80 cups.
This shows two planning errors:
- The ingredient order did not match the sales prediction - they under-bought mango relative to their own forecast.
- The forecast itself was optimistic: they sold 140 cups, not 180.
A strong answer notes that the inconsistency means the original plan could never have worked as written, regardless of how many cups were sold.
3. The teacher suggests raising the price to $5.00 next year. Using the actual numbers, would this have turned the loss-making scenario into a profit? Explain with calculations.
Read the worked answer
At $5.00 per cup with 140 cups sold: revenue = 140 × $5.00 = $700.
Costs stay at $173.20 (assuming the same purchases), so profit = $700 − $173.20 = $526.80.
Even at the lower sales figure of 140 cups, the stall was already profitable at $4.00 ($386.80). So the price rise is not needed to avoid a loss - the stall never made a loss. The real problem was waste: leftover mango and yoghurt were thrown out.
A careful answer checks the premise of the question. The teacher's suggestion assumes a loss, but the calculations show a profit. The better improvement is to buy ingredients closer to actual demand (e.g. about 21 kg mango for 140 cups at 150 g, or reduce the serving size) rather than raise prices, which might reduce sales further.