Subtraction
In this topic you will
- Subtract ones from a $2$-digit number.
- Subtract tens from a $2$-digit number.
- Identify whether to add or subtract to solve a word problem.
Key Words
- column subtraction
- operation
Show Definitions
- column subtraction: A method for subtracting numbers by lining up the digits in columns (ones under ones, tens under tens) and subtracting each column.
- operation: A mathematical action you do to numbers, such as addition, subtraction, multiplication, or division.
❓ EXERCISES
$1$. Find the missing numbers.
a. $37 - 5 =$ ____
b. $46 - 4 =$ ____
c. $79 - 6 =$ ____
d. $68 - 7 =$ ____
e. $59 - 8 =$ ____
f. $87 - 5 =$ ____
👀 Show answer
a.$37 - 5 = 32$
b.$46 - 4 = 42$
c.$79 - 6 = 73$
d.$68 - 7 = 61$
e.$59 - 8 = 51$
f.$87 - 5 = 82$
$2$. Find the missing numbers.
a. $69 - 5 =$ ____
b. $49 - 6 =$ ____
c. $78 - 7 =$ ____
👀 Show answer
a.$69 - 5 = 64$
b.$49 - 6 = 43$
c.$78 - 7 = 71$
❓ EXERCISES
$3$. Find the missing numbers.
a. $47 - 10 =$$\square$
b. $85 - 10 =$$\square$
c. $69 - 10 =$$\square$
d. $36 - 20 =$$\square$
e. $58 - 20 =$$\square$
f. $64 - 30 =$$\square$
👀 Show answer
a.$47 - 10 = 37$
b.$85 - 10 = 75$
c.$69 - 10 = 59$
d.$36 - 20 = 16$
e.$58 - 20 = 38$
f.$64 - 30 = 34$
$4$. Find the missing numbers.
a. $52 - 10$
b. $61 - 20$
c. $45 - 30$
👀 Show answer
a.$52 - 10 = 42$
b.$61 - 20 = 41$
c.$45 - 30 = 15$
🧠 Think like a Mathematician
Task: Choose a row from the bottom half of a $100$ square. Subtract $20$ from each of your numbers. What do you notice about your answers? Will the same thing happen, whichever row you choose?
Method:
- Pick any one row from the bottom half of a $100$ square (so your numbers are at least $51$).
- Write down all the numbers in that row.
- Subtract $20$ from each number.
- Look for patterns in your new row (what stayed the same, and what changed?).
- Repeat with a different bottom-half row to check if the same pattern happens again.
Reflection: Write a short explanation of what you noticed, and compare your explanation with someone else’s idea. If your explanations are different, explain why.
Show Answers
- What you should notice: Every answer is exactly $20$ less, so the tens digit goes down by $2$ while the ones digit stays the same. For example, $78 - 20 = 58$.
- What happens to the row: The results make a new row that lines up with the original row, just two rows higher on the $100$ square.
- Will it always happen? Yes, for any row in the bottom half, subtracting $20$ moves each number up by $20$ on the square (as long as you stay within $1$ to $100$).
❓ EXERCISES
5. Choose the correct operation (add or subtract) to solve each word problem. Write and solve your number sentence.
a. Dad bought a bag of $24$ red apples and a bag of $10$ green apples.
How many apples did Dad buy?
b. There are $64$ seats on the bus.
$30$ people get on.
How many empty seats are there?
c. There are $28$ pages in Arun’s book.
He read $6$ pages.
How many pages does he have left to read?
d. A baker made $32$ chocolate cookies and $20$ raspberry cookies.
How many cookies did he make altogether?
👀 Show answer
a.$24 + 10 = 34$
b.$64 - 30 = 34$
c.$28 - 6 = 22$
d.$32 + 20 = 52$
6. Tick the correct calculations. Correct any mistakes.
👀 Show answer
Correct calculations:$83 - 30 = 53$ and $42 + 7 = 49$.
Corrections:
$58 - 5 = 53$ (not $8$).
$34 + 20 = 54$ (not $34 - 20 = 14$).
❓ EXERCISES
7. Draw a ring around the calculation that does not have the same answer as the others.
$39 - 6$
$23 + 10$
$43 - 20$
$37 - 4$
👀 Show answer
Ring:$43 - 20$
$39 - 6 = 33$, $23 + 10 = 33$, and $37 - 4 = 33$, but $43 - 20 = 23$.