A quality-control step is a point in production where something is checked against a standard, and a decision follows. A good answer says what is checked, when, against what limit and what the firm does with a fault. The marks go to that chain, not to the phrase “to make sure quality is good”.
This lesson follows finding a bottleneck in operations and productivity. Later, technology, quality and sustainability takes the topic further.
What makes a quality-control step complete?
Use a four-part frame for any step.
- The check: what is looked at, measured or tasted, and at what point in the process.
- The standard: the limit that decides pass or fail, such as a minimum weight or a maximum fault rate.
- The action: what happens to items or batches that fail, such as rework, rejection or a second inspection.
- The effect: one benefit and one cost for this firm.
Firms often check a sample, which is a small number of items from a batch, because checking everything is slow and costly. The fault rate in the sample is used to estimate the fault rate in the whole batch.
Worked example
Kilang Biskut Raya Sdn Bhd packs 1,600 tins of cookies in each batch. Before the batch leaves the factory, an inspector takes 40 tins at random and opens them to check for broken cookies. The company’s limit is a fault rate of no more than 5%.
Step 1, calculate the sample fault rate. In one batch, 3 of the 40 tins have broken cookies. 3 ÷ 40 = 0.075, which is 7.5%.
Step 2, compare with the standard. 7.5% is more than the 5% limit, so the batch fails the check.
Step 3, estimate the faults in the whole batch. 7.5% of 1,600 = 0.075 × 1,600 = 120 tins. The check suggests about 120 tins with broken cookies.
Step 4, state the action. The batch is held back, and every tin is inspected, with the broken ones repacked.
Step 5, give an effect. A benefit is that customers receive fewer damaged tins, which protects the brand during the festive season. A cost is the inspector’s time and the cookies destroyed in sampling.
The mistake to watch for
A common slip is to write a general statement with no step in it.
Mistaken answer: “Quality control ensures that the cookies are of good quality so customers are happy.”
This could describe any firm. It names no check, no limit, no action and no cost.
The correction is to describe the step. “An inspector opens 40 random tins from each 1,600-tin batch. If more than 5% have broken cookies, the batch is held back and checked tin by tin. This protects the firm’s reputation but costs inspector time and some tins.”
Every part of this sentence is tied to the case.
Check yourself
Try these on paper, then open each answer.
1. An inspector tests 200 bottles and finds 6 faulty. Calculate the fault rate.
Show answer
6 ÷ 200 = 0.03, so the fault rate is 3%.
2. A batch holds 2,000 bottles, and a sample of 50 has 4 faulty. Estimate the faulty bottles in the batch, and say whether the batch passes a 5% limit.
Show answer
Sample rate: 4 ÷ 50 = 0.08, which is 8%. Estimate: 0.08 × 2,000 = 160 bottles. Since 8% is above 5%, the batch fails the limit.
3. Explain why a firm making sealed tins of sardines tests a sample, not every tin.
Show answer
Testing a tin means opening it, so the tested tin cannot be sold. Testing every tin would destroy the whole batch. A sample gives an estimate of the fault rate at a much lower cost.
Where this leads next
Now see how a firm decides how much stock to hold in comparing inventory choices using stated constraints, and test the whole module with the operations practice set. The ratios tool can check a fault-rate division.
Some students describe the check well but cannot say what the firm should do next. A teacher in online one-to-one Business tuition can help you build the habit of finishing every quality answer with an action.