# Attention P4s and P5s! - Must know concept before your SA2!

### Shortage and Surplus Step-by-Step approach (P3-P5 Question)

Over the years, our trainers have identified such question to be a common question for exams. Shortage and Surplus happens when there are two scenarios in one question. How to solve it through our Matrix Method step-by-step approach? Read on to find out!

Example:

*Yenni wants to buy some hair clips. If she buys 9 similar hair clips, she will have $6 left. If she buys 12 similar hair clips, she will need another $9 more. What is the amount of money Yenni have at first?*

Step 1: Draw 2 equal models (to illustrate the total amount of money Yenni has is unchanged )

Step 2: Record 1st set of data for the first model (Look for keywords like “need”, “left”, “leftover”)

1st key information: if she buys 9 hair clips, have $6 left. (“left” means Yenni has the amount of money with her)

Step 3: Record the second set of data for the 2nd model. (Look for keywords like “need”, “left”, “leftover”)

2nd key information: If she buys 12 similar hair clips, she will need another $9 more. (“need” means Yenni do not have the amount of money, hence dotted lines to indicate Yenni need extra, not from the original amount she had)

Step 4: Compare the two models and the difference in objects and cost.

**Hence,**

3 hair clips-> $6 + $9

= $15

1 hair clip -> $15 ÷ 3

= $5

Amount of money Yenni have at first = model’s solid box

Using 1st model to solve,

9 hair clips -> $5 × 9

= $45

Amount of money Yenni have at first -> $45 + 6

= $51

**Using 2nd model to solve,**

12 hair clips-> $5 × 12

= $60

Amount of money Yenni have at first-> $60 − 9

= $51

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