Question 1
Round each factor to the nearest ten, then multiply: 47 × 31.
What is the approximate value?
- 1496
- 1500
- 1457
- 1492
- 1410
Show the worked solution
- 47 → 50, 31 → 30.
- 50 × 30 = 1500.
- Answer: 1500.
Exam path · Approximation
Approximation questions, rounded before you calculate
Approximation questions ask for a value close to the exact answer, not the exact answer itself, so the fast route is to round every number before you calculate rather than after. Round each addend to the nearest ten and add, round each factor to the nearest ten and multiply, or round a percentage to the nearest five before applying it — then stop, because the rounded figure already is the answer.
Approximation sits right beside simplification on a bank paper and shares its whole appeal: it is a fixed procedure rather than a problem to think through, so speed comes from habit, not cleverness. The trap the setter relies on is the exact value — calculating it in full costs time the rounded version never needed, and the exact figure is printed as a wrong option on purpose.
Try it against the clock. Approximation runs at 20s easy, 30s medium and 40s hard. The clock is stamped and judged on our server, so the limit you see is the deadline that is actually enforced — and it starts when you tap Start, not while the question is loading.
How to solve approximation questions by rounding first
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Round every number before you touch the operation
47 + 82 + 19 becomes 50 + 80 + 20 before any addition happens. Rounding after adding defeats the entire point — the exact sum is what the question is asking you to avoid computing.
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Round each factor to the nearest ten for multiplication
49 × 21 rounds to 50 × 20 = 1000, found without multiplying either original number.
-
Round a percentage to the nearest five before applying it
16% of 200 rounds to 15% of 200 = 30. Percentages round to the nearest 5, not the nearest 10, because most bank-exam percentage figures already sit near a multiple of 5.
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Stop at the rounded figure — do not correct back toward the exact value
The rounded answer is the one the question wants, and options are built so the exact value sits nearby as the wrong pick, not the right one.
Three shapes of the same question
| What the paper asks | The move |
|---|---|
| Round and add three numbers | Round each addend to the nearest ten, then add |
| Round and multiply two numbers | Round each factor to the nearest ten, then multiply |
| Find an approximate percentage of a number | Round the percent to the nearest 5, then apply it |
3 real approximation questions, with worked solutions
Generated by the same engine that mints the ComputePrep daily. Each answer is computed from the numbers printed in the question, and the walkthrough below each one is the engine's own working — not a solution written afterwards. Reload this page's live drill and you get different numbers.
Question 2
Round each factor to the nearest ten, then multiply: 47 × 22.
What is the approximate value?
- 1100
- 1000
- 940
- 1034
- 1014
Show the worked solution
- 47 → 50, 22 → 20.
- 50 × 20 = 1000.
- Answer: 1000.
Question 3
Round each factor to the nearest ten, then multiply: 51 × 28.
What is the approximate value?
- 1400
- 1486
- 1428
- 1500
- 1530
Show the worked solution
- 51 → 50, 28 → 30.
- 50 × 30 = 1500.
- Answer: 1500.
Common mistakes this drill is built from
The wrong options are not random numbers. Each one is the result of a specific careless error for this topic, so picking one tells you which habit is costing you marks.
Calculating the exact value first
49 × 21 = 1029 exactly, but the rounded answer is 1000. Doing the full multiplication and then rounding the result wastes the time approximation exists to save, and the exact figure is usually printed as a distractor.
Rounding only one number in the expression
47 + 82 + 19 rounded on just the first term gives 50 + 82 + 19 = 151, a near miss that is close enough to the correct 150 to look right. Round every term, not just the easy one.
Rounding a percentage to the nearest 10 instead of 5
16% rounds to 15%, not 20%. Percentage figures in this topic are built to sit near a multiple of 5, and rounding to the nearest 10 overshoots by a wider margin than the question allows.
Why your answer came out wrong
The specific wrong numbers this topic produces, and what each one tells you about the step you took. If you have just got a question wrong and want to know which habit did it, start here.
47 + 82 + 19 rounds to what — why isn't it 148?
148 is the exact sum, not the approximation. Round each term first: 47→50, 82→80, 19→20, then add: 50+80+20=150. Adding the unrounded figures and only then rounding defeats the method — round first, every time.
49 × 21 — why isn't the approximate answer 1029?
1029 is the exact product. Round each factor to the nearest ten first — 49→50, 21→20 — then multiply: 50×20=1000. The exact figure is always sitting on the board as the tempting wrong option.
16% of 200 — why isn't the approximate answer 32?
32 is the exact value. Round the percentage to the nearest five first — 16%→15% — then apply it: 15% of 200 = 30. Rounding after calculating, instead of before, is what produces the exact figure instead of the approximation.
FAQ
What is the fastest method for approximation questions?
Round every number in the expression before you calculate, not after — to the nearest ten for addition and multiplication, or the nearest five for a percentage. The rounded figures are what you operate on; the exact value is never needed.
How long should an approximation question take in prelims?
Between 20 and 40 seconds. This drill enforces exactly that: 20 seconds on easy, 30 on medium and 40 on hard, timed on the server rather than in your browser.
Should I round to the nearest 10 or the nearest 5?
Nearest 10 for plain numbers being added or multiplied, nearest 5 for a percentage. The distinction exists because most exam percentage figures already sit close to a multiple of 5, so rounding further would move the answer too far.
Is approximation the same as simplification?
They sit next to each other on the paper and share the same speed habit, but simplification wants an exact value under BODMAS while approximation deliberately asks for a rounded one — calculating the exact figure in an approximation question is the main way marks are lost.
Practise the next topic
- All 30 drill types — the full rotation with every published time limit.
- Simplification questions — BODMAS — simplification questions, timed.
- Percentage questions for bank exam papers — percentage questions for bank exam, timed.
- Fast calculation questions — the mental arithmetic the clock actually tests — fast calculation questions, timed.
- Vedic maths shortcuts — the seven sutras that make a 15-second answer possible.
- How to improve calculation speed — the six-week arc these drills fit into.
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