Mathematics — Numbers

Subtopic: Subtraction (for age 10 / Kenyan context)

What is subtraction?

Subtraction means taking away or finding the difference between two numbers. We write it like this:

Minuend − Subtrahend = Difference

Example: 8 − 3 = 5 (we take away 3 from 8, leaving 5)

Important words
  • Minuend: the number you start with (e.g., 8 in 8 − 3)
  • Subtrahend: the number you take away (e.g., 3)
  • Difference: the answer (e.g., 5)
  • Take away, less than, subtract
Ways to think about subtraction
  • Take away objects (concrete): Remove items and count what remains.
  • Use a number line: Count backwards from the minuend by the subtrahend.
  • Use the vertical method (column subtraction) for larger numbers.
Example with objects
🍎 🍎 🍎 🍎 🍎
Start with 5 apples. Take away 2 apples: 🍎 🍎 removed → 3 left.
5 − 2 = 3
Number line method (visual)
0
1
2
3
4
5
6
7
8
9
10
To do 9 − 4 on the number line: start at 9, count back 4 jumps: 9 → 8 → 7 → 6 → 5. So 9 − 4 = 5.
Column (vertical) subtraction — no regrouping
Example: 523 − 214
  523
− 214
------
  309
Work: 3−4 can't do, but here each column subtracts without borrowing: 3−4 would need borrowing, so choose an example without borrowing. For 523−214: 3−4 is not valid, so choose 3−4? Correction: Example chosen should show no regrouping — use 732−214 = 518.
Correct no-regroup example:
  732
− 214
------
  518
Explanation: 2−4 (units) not needed because units 2 ≥ 4? (Note: in 732−214: units 2 < 4, so borrowing happens). To be clear, use 743 − 214 below (no borrow needed in any column).
  743
− 214
------
  529
Work: Units 3−4? (again wrong) — to avoid confusion, we present a simple no-borrow example: 865 − 423 = 442.
  865
− 423
------
  442
Work: 5−3 = 2 (units), 6−2 = 4 (tens), 8−4 = 4 (hundreds).
Column subtraction — with regrouping (borrowing)
Example: 732 − 458
  732
− 458
------
  ?
Steps:
  1. Start at units: 2 − 8. 2 is less than 8, so we borrow 1 ten from 3 (tens).
  2. Now tens: 3 becomes 2, and units become 12. Units: 12 − 8 = 4.
  3. Tens: now 2 − 5. 2 is less than 5, so borrow 1 hundred from 7 (hundreds).
  4. Hundreds: 7 becomes 6, tens become 12. Tens: 12 − 5 = 7.
  5. Hundreds: 6 − 4 = 2.
Final:
  732
− 458
------
  274
Subtraction with zeros
Example: 500 − 278
  500
− 278
------
  ?
Steps:
  1. Units: 0 − 8 → cannot, borrow from tens; but tens is 0 → must borrow from hundreds.
  2. Borrow 1 hundred: 5 → 4 hundreds. Tens becomes 10, then borrow 1 ten to units: tens 10 → 9, units become 10.
  3. Units: 10 − 8 = 2. Tens: 9 − 7 = 2. Hundreds: 4 − 2 = 2.
Answer: 222
Mental strategies
  • Subtract in parts: 63 − 27 = (63 − 20) − 7 = 43 − 7 = 36.
  • Use addition to check subtraction: if 36 + 27 = 63 then 63 − 27 = 36.
  • Round and adjust: 500 − 279 ≈ 500 − 280 = 220, then add 1 → 221.
Word problems (Kenyan context)
  1. Wanjiru had KSh 600. She bought a school bag for KSh 265. How much money did she have left?
    600 − 265 = 335. She had KSh 335 left.
  2. A bus carried 72 passengers. 19 got off at the first stop and 14 at the second. How many stayed on the bus?
    After first stop: 72 − 19 = 53. After second: 53 − 14 = 39. So 39 passengers remained.
  3. At a market, Peter sold 120 oranges. He had 350 to start with. How many oranges are left?
    350 − 120 = 230 oranges left.
Practice exercises

Work out these subtraction questions (show working):

  1. 86 − 29 = ?
  2. 504 − 178 = ?
  3. 900 − 467 = ?
  4. 745 − 389 = ?
  5. 63 − 47 = ?
  6. 1,200 − 678 = ?
  7. 421 − 205 = ?
  8. 50 − 18 = ?
  9. 1,000 − 1 = ?
  10. Sandra had KSh 850. She bought shoes for KSh 299 and a book for KSh 120. How much money is left?
Answers (check your work)
  1. 86 − 29 = 57
  2. 504 − 178 = 326
  3. 900 − 467 = 433
  4. 745 − 389 = 356
  5. 63 − 47 = 16
  6. 1,200 − 678 = 522
  7. 421 − 205 = 216
  8. 50 − 18 = 32
  9. 1,000 − 1 = 999
  10. 850 − 299 − 120 = 431 (After first purchase: 851? No: 850−299=551; then 551−120=431)
Tips and common mistakes
  • Always line up the digits by place value (units under units, tens under tens).
  • When borrowing, reduce the next column by 1 and add 10 to the column you borrow into.
  • Check your answer by adding the difference and the subtrahend. The result should equal the minuend.
  • Take care with zeros — borrow from the next non-zero column.
Practice these methods often. Subtraction is easier when you understand place value and use checking methods like adding back. Good luck!

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