Viral Maths — Ch03: Subtraction

📌 What This Chapter Covers

Subtraction is all about finding the GAP between two numbers.
The book uses a vegetable vendor as an example because subtraction is used very frequently in a shop. Practise daily and calculate verbally.
There are eight named approaches. Choose the correct one by examining the shape and closeness of the numbers.

⚡ QUICK RECALL

Selection guide: 2-digit − 1-digit → Todu-Modu; mirror numbers → Sita-Gita; number near 100/200/300 → Tidding-Tidding; both numbers near the same base → Nadiya Paar; mixed +/− chain → Anti-Bodmas; subtract FROM 100/1000 → Sabji Wala; subtract from 50 (20s) → Bhai Bhai; close final two digits → Last-2-Digit Fix Method.

🗂️ Chapter Index

Tab	Approach	Best For
2	Todu-Modu	2-3 digit number − 1-digit number
3	Sita-Gita (Judwa)	Number − its digit-reversal (mirror)
4	Tidding-Tidding	Subtrahend close to 100/200/300...
5	Nadiya Paar	Both numbers close to the SAME base
6	Anti-Bodmas	Mixed addition-subtraction chains
7	Sabji Wala (Century)	100/1000/multiples MINUS a number
8	Bhai Bhai	50 minus a number in the 20s
9	Last-2-Digit Fix	Big numbers whose last 2 digits are close
10	Master Table	All 8 approaches summarized

Type 1 — Todu-Modu Approach

Break the number being subtracted (using the units digit of the first number) into two convenient parts.

Example: 83 − 7

Break 7 as (3+4) using unit digit of 83 Step 1: 83 − 3 = 80 Step 2: 80 − 4 = 76

Example: 87 − 9

Break 9 as (7+2) using unit digit of 87 Step 1: 87 − 7 = 80 Step 2: 80 − 2 = 78

⚡ QUICK RECALL

First remove the units digit from the first number to make a round number, then subtract the remainder. The calculation is completed in two short steps.

Type 2(a) — Sita-Gita (Judwa) Approach — 2-digit Mirror

Use when: a 2-digit number is subtracted from its digit-reversal (Judwa pair)

Example: 63 − 36

Step 1: Difference between digits: 6−3 = 3 Step 2: Multiply always by 9: 3×9 = 27

⚡ QUICK RECALL

2-digit mirror subtraction = (digit difference) × 9 — always.

Type 2(b) — Sita-Gita Approach — 3-digit Mirror

Use when: a 3-digit number is subtracted from its digit-reversal (middle digit stays fixed)

Example: 652 − 256

Step 1: Difference between FIRST and LAST digit: 6−2 = 4 Step 2: Multiply always by 99: 4×99 = 396

⚠ EXAM TRAP

The multiplier for three-digit mirror subtraction is 99, while the multiplier for two-digit mirror subtraction is 9. Use only the difference between the FIRST and LAST digits; ignore the middle digit because it cancels automatically.

Type 3 — Tidding-Tidding Approach (Subtrahend Near a Base)

Use when: the number BEING SUBTRACTED is close to 100, 200, 300...

Example: 167 − 96

Consider 96 as 100 (4 extra) Step 1: Subtract 100 from 167: 67 Step 2: Add back the extra: 67+4 = 71

Example: 667 − 293

Consider 293 as 300 (7 extra) Step 1: Subtract 300 from 667: 367 Step 2: Add back extra: 367+7 = 374

⚡ QUICK RECALL

Round the SUBTRAHEND up to its nearest base, subtract that clean base, then ADD BACK the extra you over-subtracted.

Type 4 — Nadiya Paar Approach (Both Numbers Near Same Base)

Use when: BOTH numbers are close to the same base (100, 200, 300...) — find each number's margin from that base and ADD the margins

Example: 915 − 888 (base = 900)

Step 1: 915 is 15 above 900 Step 2: 888 is 12 below 900 Add the margins: 15+12 = 27

Example: 1205 − 778 (base = 800)

Step 1: 1205 is 405 above 800 Step 2: 778 is 22 below 800 Add margins: 405+22 = 427

⚠ EXAM TRAP

In “Nadiya Paar” (crossing the river), the two numbers must lie on opposite banks of the same base—one above and one below. If both are on the same side of the base, subtract the margins instead of adding them.

⚡ QUICK RECALL

If one number is above the base (+margin) and the other is below it (−margin), simply ADD the two margins.

Type 5 — Anti-Bodmas Approach (Reorder for Easy Subtraction)

It's not necessary to always calculate left-to-right — if two numbers in the chain are close to each other, subtract them FIRST

Example: 25 + 63 − 65

Step 1: 63 and 65 are close → do this first: 63−65 = −2 Step 2: Add to 25: 25+(−2) = 23

Example: −267 + 196 + 253

Step 1: 253 and 267 are close → 253−267 = −14 Step 2: Add to 196: 196−14 = 182

⚡ QUICK RECALL

Scan the entire expression and handle the two closest numbers first; the rest then becomes simple. This is the subtraction version of the Giddh Approach used in Addition.

Type 6 — Sabji Wala / Century Approach (100/1000 − Number)

Use when: subtracting a number FROM 100, 1000, or their multiples

Example: 100 − 36 (Method A — build up)

Try to make 36 reach 100: Step 1: Add 4 to 36 → 40 Step 2: Add 60 to 40 → 100 Total added: 4+60 = 64 (Answer)

Example: 100 − 36 (Method B — break and subtract)

36 = 30+6 Step 1: 100−30 = 70 Step 2: 70−6 = 64

Example: 1000 − 357

357 = 300+50+7 Step 1: 1000−300 = 700 Step 2: 700−50 = 650 Step 3: 650−7 = 643

⚡ QUICK RECALL

This is the same method a vegetable vendor uses while giving change: split the number into place-value parts and subtract them from the base one by one.

Type 7 — Bhai Bhai Approach (50 − Number in 20s)

Rule: Whenever subtracting a number in the 20s (21, 22, 23...) from 50, the answer is always in the 20s too

Formula

Tens place of answer = always 2 Units place of answer = 10 − (units digit of subtracted number)

Example: 50 − 26

Tens place = 2 Units place = 10−6 = 4 Answer: 24

Example: 50 − 28

Tens place = 2 Units place = 10−8 = 2 Answer: 22

⚠ EXAM TRAP

In “Bhai Bhai” (brothers), both numbers belong to the 20s family: the number being subtracted and the answer are both in the twenties. This works only when subtracting from 50, not from any other base.

Type 8 — Last-2-Digit Proximity Method

Use when: two big numbers being subtracted have last-2-digits that are close to each other

Example: 4449 − 3051

Step 1: Add a convenient base (1400) to smaller number (3051) to get close to 4449: 3051+1400 = 4451 Step 2: Now you're 2 steps AHEAD of 4449 (4451 vs 4449) Step 3: Subtract that overshoot from your base: 1400−2 = 1398 (Answer)

⚡ QUICK RECALL

Guess a round gap (like 1400) between the two numbers, add it to the smaller number, see how far off you land from the bigger number, then correct the guessed gap by that overshoot/undershoot.

⚠ EXAM TRAP

If the guessed result is GREATER than the target, SUBTRACT the overshoot from the base, as in the example. If it is SMALLER, ADD the undershoot to the base.

📋 Master Table — All Subtraction Approaches

Approach	When to Use	Core Rule
Todu-Modu	Number − 1-digit	Break subtrahend using first number's unit digit
Sita-Gita (2-digit)	Number − its mirror	(digit difference) × 9
Sita-Gita (3-digit)	Number − its mirror	(first−last digit difference) × 99
Tidding-Tidding	Subtrahend near a base	Subtract full base, add back the extra
Nadiya Paar	Both numbers near same base	Add the two margins from base
Anti-Bodmas	Mixed +/− chain	Subtract closest pair first, then combine
Sabji Wala (Century)	100/1000/multiple − number	Break subtrahend by place value, subtract stepwise
Bhai Bhai	50 − (20s number)	Tens=2, Units=10−unit digit
Last-2-Digit Fix	Big numbers, close last-2-digits	Guess round gap, add to smaller, correct by overshoot

🔑 Approach Selection Flowchart

Subtracting a single digit → Todu-Modu
Number − its own digit-reversal → Sita-Gita (Judwa)
Only the subtrahend is near a round base → Tidding-Tidding
BOTH numbers are near the SAME round base → Nadiya Paar
Chain of + and − with two close numbers in it → Anti-Bodmas
Subtracting FROM 100/1000/multiples → Sabji Wala
50 minus a 20s number → Bhai Bhai
Big 4-digit numbers with close last-2-digits → Last-2-Digit Fix