seegongsik
Grade 4 (age 9-10)

grade 4 Fraction Addition & Subtraction

Fractions with the same denominator are easy to add and subtract. The denominator tells the size of each piece, so it stays the same; you only add or subtract the numerators, which count the pieces. Cut a cake into 6 slices: if you eat 2 and a friend eats 3, together you ate 2/6 + 3/6 = 5/6 of the cake. Change the denominator and the two numerators and choose addition or subtraction; the three bars, split into equal parts, and the fraction equation change together.

Adding Like Fractions

🍰 Think of a Cake
①Cut a whole cake into 6 equal slices, and each slice is 1/6
②If you eat 2 slices and a friend eats 3, you ate 5 slices together
③So 2/6 + 3/6 = 5/6
④The slices stay the same size, so the denominator 6 does not change

Seeing It on Bars

6
2
3

Checking with the Equation

💡 Calculating Like Fractions
①With the same denominator, add or subtract only the numerators
②Adding the denominators too would turn 2/6 + 3/6 into 5/12, which is even less than your friend's 3/6, so it cannot be right
③Subtraction works the same way: 5/6 − 3/6 = 2/6
④In the picture, the two numerators never add up to more than the denominator, so the answer fits inside one bar

Summary

Adding Like Fractions
ac + bc = a+bc
Keep the denominator and add the numerators
Subtracting Like Fractions
ac − bc = a−bc
Keep the denominator and subtract the numerators
Watch Out
Never add the denominators
The denominator is the size of each piece, so adding or subtracting does not change it
🎯 Summary
①Like fractions are added or subtracted by working with the numerators only
②The denominator is the size of each piece, so it stays the same
③Adding the denominators gives a strange answer that is too small
④If a sum is bigger than 1, it can be written as a mixed number
⑤Fractions with different denominators are added after making the denominators the same

Examples and Unit Test

Example 1
Add 2/7 + 3/7.
1
The denominators are both 7, so add the numerators: 2 + 3 = 5.
2
Keep the denominator 7, so the answer is 5/7.
▸ 57 (five-sevenths)
2 slices and 3 slices out of 7 make 5 slices.
Example 2
Subtract 5/8 − 2/8.
1
The denominators are both 8, so subtract the numerators: 5 − 2 = 3.
2
Keep the denominator 8, so the answer is 3/8.
▸ 38 (three-eighths)
Taking 2 slices away from 5 slices out of 8 leaves 3 slices.
Unit Test
What is 1/6 + 4/6?
①512
②56
③46
④536
▸ ② 56
1
The denominators match, so add the numerators: 1 + 4 = 5.
2
Keep the denominator 6, so the answer is 5/6. Adding the denominators, as in ①, is wrong.
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Multi-digit Multiplication
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Understanding Decimals

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