how are these math answers incorrect?

Question

we did peer evaluation in class and the math teacher wrote the answers on the board. the following questions i got wrong. but i dont understand how. are these answers right or did my math teacher miscalculate.?

2/3 +3/4 i got 15/12 and in simplified form i got 1 1/4

2/3 + 5/6 i got 9/6 and in simplified form i got 1 1/2

1 1/6 + 2 1/2 i got 88/ 12 in simpilfied i got 9 1/3

1 1/3 + 2 3/8 i got 157/24 in simpilfied for i got 6 13/ 24

please explain

Answer 1

2/3 + 3/4 you need to find a common denominator

8/12 + 9/12 = 17/12 simplified 1 5/12

2/3 + 5/6 you need to find a common denominator

4/6 + 5/6 = 9/6 simplified 1 3/6 or 1 1/2

7/6 + 5/2 you need to find a common denominator

7/6 + 15/6 = 22/6 simplified 3 4/6 or 3 2/3

4/3 + 19/8 you need to find a common denominator

32/24 + 57/24 = 89/24 simplified 3 17/24

Answer 2

The first one seems to have been a simple arithmetic error - 8+9 = 17, not 15.

The second one is correct, as others have said.

For the last two, you are not handling your mixed fractions correctly. For instance, 1 1/3 + 2 3/8: you are taking this to be 11/3 + 23/8, which is not at all the same thing. You need to convert mixed fractions to improper fractions first, then find the lowest common denominator and add. So 2 3/8 = (2*8+3) / 8 = 19/8, and 1 1/3 = 4/3, so we have
4/3 + 19/8 = (4*8 + 19*3) / (3*8) = (32 + 57) / 24 = 89/24 = 3 17/24.

Also, note that in the third question, 88/12 is not equal to 9 1/3. 88/12 = 22/3 = 7 1/3.

Answer 3

2/3 + 3/4 = 8/12 + 9/12 = 17/12

2/3 + 5/6 = 8/12 + 10/12 = 18/12 = 9/6

1 1/6 + 2 1/2 = 7/6 + 5/2 = 7/6 + 15/6 = 22/6 = 11/3

1 1/3 + 2 3/8 = 4/3 + 19/8 = 32/24 + 57/24 = 89/24

Answer 4

8/12 + 9/12 = 17/12 = 1 5/12
4/6 +5/6 = 9/6 = 1 1/2
7/6 +5/2 = 7/6 + 15/6 = 22/6 = 3 4/6 = 3 2/3
4/3 + 19/8 = 32/24 = 57/24 = 89/24 = 3 17/24

I think number 2 is correct the others do not appear to be.....

Answer 5

2/3 + 3/4 = 17/12

2/3 + 5/6 = 3/2

1/1/6 + 2/1/2 = ((1*6+1) =7) = 7/6 ((2*2+1) = 5) = 5/2 = 11/3 = 3/2/3

1/1/3 + 2/3/8 = 4/3 + 19/8 = 89/24

Answer 6

2/3 +3/4 changes to 8/12 + 9/12 which equals 17/12

2/3 + 5/6 changes to 4/6 + 5/6; so that one you got right

1 1/6 + 2 1/2 changes to 7/6 + 5/2 which then changes to
7/6 + 15/6 which equals 22/6

1 1/3 + 2 3/8 changes to 4/3 + 19/8

Answer 7

first one is 17/12

the second one is corect

the third one is 22/6

the 4th is 32/24+19/24= 51/24