The On-Screen Calculator: When and How to Use It

The preceding lessons have emphasised mental arithmetic and estimation. This lesson covers the flip side: how to use the on-screen calculator effectively when you do need it. Understanding the calculator's quirks — especially the BODMAS issue — and knowing when it genuinely saves time will make you a more efficient QR candidate.

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What the Calculator Offers

The UCAT on-screen calculator has:

• Digit buttons: 0–9 and a decimal point
• Operations: +, −, ×, ÷
• Equals: =
• Memory functions: M+, M−, MR (Memory Recall), MC (Memory Clear)
• Square root: √
• Percentage: %
• Clear: C (clears current entry), CE/AC (clears everything)

It does not have:

• Brackets
• Trigonometric functions
• Logarithms
• An exponent/power button
• A backspace/undo button

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The BODMAS Problem: How the Calculator Actually Works

This is the most important thing to understand about the UCAT calculator.

Standard Mathematics (BODMAS)

In standard mathematics, the order of operations is:

1. Brackets
2. Orders (powers, roots)
3. Division and Multiplication (left to right)
4. Addition and Subtraction (left to right)

So 3 + 4 × 5 = 3 + 20 = 23.

The UCAT Calculator (Sequential)

The UCAT calculator processes operations in the order you enter them, with no regard for BODMAS.

So if you type 3 + 4 × 5 =, the calculator computes:

1. 3 + 4 = 7
2. 7 × 5 = 35

This is wrong mathematically but is how the calculator behaves.

Why This Matters

Many QR calculations involve multiple operations. If you type them directly into the calculator, you will get the wrong answer unless you control the order manually.

Example: You need to calculate (12 × 4.50) + (8 × 3.25).

If you type: 12 × 4.50 + 8 × 3.25 =

The calculator computes:

1. 12 × 4.50 = 54
2. 54 + 8 = 62
3. 62 × 3.25 = 201.5 ✗

The correct answer is 54 + 26 = 80 ✓.

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Strategy: Break Calculations into Steps

Since the calculator does not handle BODMAS, you must break multi-step calculations into separate steps and use the memory function to store intermediate results.

The Step-by-Step Method

1. Calculate the first sub-expression
2. Store it in memory (M+)
3. Clear the display
4. Calculate the second sub-expression
5. Add to memory (M+) or subtract from memory (M−)
6. Recall the memory (MR) for the final answer

Worked Example: Using Memory

Calculation: (12 × 4.50) + (8 × 3.25)

Step	Key Presses	Display	Memory
1	12 × 4.5 =	54	0
2	M+	54	54
3	8 × 3.25 =	26	54
4	M+	26	80
5	MR	80	80
6	MC (clear memory for next question)	80	0

This produces the correct answer: 80.

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The Memory Functions Explained

Button	Function	When to Use
M+	Adds the displayed value to memory	Store a sub-total you want to add later
M−	Subtracts the displayed value from memory	Store a sub-total you want to subtract later
MR	Displays the current memory value	Retrieve your stored result
MC	Clears the memory to zero	Before starting a new calculation

Critical Habit: Always Clear Memory

Press MC at the start of every new question. If memory contains a value from a previous calculation, M+ will add to it, producing a wrong answer.

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When the Calculator Is Faster Than Mental Maths

Situations Favouring the Calculator

Situation	Example	Why Calculator Wins
Multiplying two non-round numbers	347 × 28	Too many partial products mentally
Dividing by a "difficult" divisor	5,231 ÷ 17	Cannot simplify easily
Long decimal multiplication	34.75 × 18.4	Tracking decimal places is error-prone
Options very close together	234.5, 237.8, 241.2, 244.6	Need precision, not estimation
Three or more operations	(a × b) + (c × d) − e	Too many numbers to hold in working memory

Situations Favouring Mental Maths