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30 Second Check

ABAKO — 30-Second Check page · v1.5 preview
The ABAKO 30-Second Check

See the 30-Second Check in action.

A plausible answer. A quick check. A mistake corrected before submission.

Solve → Check → Compare → Correct
Quadratic equation Table check

The answer was right. It was only half the answer.

Solve x² = 2x.
Student answer

x = 2 — after dividing both sides by x.

Quick check

Use TABLE to compare f(x) = x² and g(x) = 2x. At x = 0 both columns read 0 — a solution the working never produced.

Correction

x² − 2x = 0, so x(x − 2) = 0 and x = 0 or x = 2. Dividing by x had destroyed a root.

AB-991EX display in table mode. Column x reads minus 2, minus 1, 0, 1. Column f of x reads 4, 1, 0, 1. Column g of x reads minus 4, minus 2, 0, 2.

AB-991EX, photographed. Table mode with f(x) = x² and g(x) = 2x. Row 3 shows both functions equal to 0 at x = 0 — the root that dividing by x removes.

ABAKO AB-991EX scientific calculator

What just happened?

The calculator gave a signal to go back.

It did not locate the mistake for the student. It showed that the manual answer needed another look.
1

Solve

Work through the question manually and show the required method.

2

Check

Use the AB-991EX to test the answer or solve through a different route.

3

Compare

If the results disagree, stop. Something in the question or working needs attention.

4

Correct

Find the error, fix it and check again before submitting.

Then confirm units, accuracy, required form and all required solutions.

Two more examples

Different questions. The same habit.

Linear equation

A bracket sign changes the answer.

Solve 45 − (x + 3) = 2x.
Student answer

x = 16, after changing −(x + 3) to −x + 3.

AB-991EX check

x = 14. The student returns to the bracket sign.

Key route — verify on the device
Enter equation SHIFT CALC / SOLVE 9 =
Quadratic equation

One root is not the complete answer.

Solve 5x² + x − 7 = 0, giving each solution correct to 2 d.p.
Incomplete answer

x = 1.09 only.

AB-991EX check

x = 1.09 and x = −1.29. The second root is added.

Key route — verify on the device
MENU Equation / Func Polynomial Degree 2 5 1 −7

What it can help reveal

Small slips that can cost real marks.

  • Signs and brackets
  • Arithmetic and copied values
  • Missing roots or solutions
  • Rounding and final form

What it does not replace

A better finish—not a shortcut.

The calculator gives a warning signal. The student still has to understand the question, show the mathematics and correct the working.

  • Understand the method.
  • Show required working.
  • Read final-answer instructions.

Make it useful

One habit. Two clear next steps.

For students

Protect the marks you already know how to earn.

Practise the check until it becomes part of how you finish a question.

Explore the AB-991EX
For teachers

Turn checking into a teachable classroom habit.

Learn how ABAKO can support the use of the 30-Second Check in your classroom.

Talk to ABAKO
Ahmed Saya, mathematics educator, speaking to camera

Ahmed Saya Mathematics educator · Winner, 2019 Cambridge Dedicated Teacher Awards
Why students who understand the concept still lose marks · 50 seconds

Cambridge examiner guidance

“Candidates should use calculators as checking tools in these cases.”
Additional Mathematics 4037/21 · Principal Examiner Report · June 2024

The ABAKO principle

Use the calculator to question an answer—not to replace the mathematics.

Solve first. Then check, compare, correct and confirm the final answer requirements.

Build the habit

Use the 30-Second Check with the AB-991EX.

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ABAKO AB-991EX scientific calculator

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