I did 2/3 + 1/3 I got 3/3.

How do I do 7/15 + 9/20?
I'm not good at adding fraction with different denominators.

Your first problem is correct.

When you add fractions with different denominators, you need to find a common denominator.

One way to find this common denominator is to count by 15 and by 20 til you come to the first number that is divisible by both.

15, 30, 45, 60, 75, 90 . . .
20, 40, 60, 80, . . .

Since 60/15 = 4, multiply both the numerator and denominator by 4.

7/15 = 28/60
9/20 = 27/60

28/60 + 27/60 = 55/60 = 11/12

You make the denominator the same by finding a number that will divide both 15 and 20 evenly, then change the numerators to match.

(7/15) = (28/60)
(9/20) = (27/60)
Then you can add the numerators 28+27=55 and the denominator is 60 for 55/60. Now 5 will reduce both 55 and 60 to give 11/12. Check my work.

Thank You

Adding fractions with different denominators can be a bit tricky, but you can follow these steps to do it correctly:

Step 1: Find the least common denominator (LCD) of the two fractions. This is the smallest multiple that both denominators evenly divide into. In this case, the denominators are 15 and 20.

To find the LCD, you can start by listing the multiples of each denominator:
Multiples of 15: 15, 30, 45, 60, 75, ...
Multiples of 20: 20, 40, 60, 80, 100, ...

Here, 60 is the smallest multiple that both 15 and 20 divide into. Therefore, the LCD is 60.

Step 2: Rewrite each fraction with the LCD as its new denominator.

For the fraction 7/15, we need to multiply both the numerator and denominator by a number that will give us the LCD of 60. Since the original denominator is 15 and the LCD is 60, we need to multiply the numerator and denominator by 4:
7/15 = (7 * 4) / (15 * 4) = 28/60

For the fraction 9/20, we need to multiply both the numerator and denominator by a number that will give us the LCD of 60. Since the original denominator is 20 and the LCD is 60, we need to multiply the numerator and denominator by 3:
9/20 = (9 * 3) / (20 * 3) = 27/60

Step 3: Add the rewritten fractions together.

Now that both fractions have the same denominator, you can add them together:
28/60 + 27/60 = (28 + 27)/60 = 55/60

Step 4: Simplify the fraction, if needed.

In this case, 55/60 can be simplified by dividing both the numerator and denominator by their greatest common divisor (GCD). The GCD of 55 and 60 is 5:
55/60 = (55 ÷ 5) / (60 ÷ 5) = 11/12

So, the sum of 7/15 and 9/20 is 11/12.