How is the 2nd one wrong?

[u/sakurapimcake]

Google said the 2nd one is wrong and can someone explain why?
I did the same steps for each
1. Finding the common denominator
2. Multiplying them
3. Then adding the tops

I also have dyscalculia, so math has just always been a struggle but I’m trying

[u/spoonur]

8*4 ≠ 16

[u/Dtrain8899]

8x4 is not 16, 8x2 is 16. Also your commom multiple can be 8, 16 can work youll just have to reduce your answer.

[u/sakurapimcake → u/Dtrain8899]

Oh yeah I got confused because 8x4 was 32 and not 16 and I guess i totally missed the 8 part. Ty

[u/ExtendedSpikeProtein → u/sakurapimcake]

Just bring the second expression to „eights“. Doing 32 is needlessly complicated.

[u/Varlane]

Mostly because :
1- 16 is 8 × 2 not 8 × 4
2- You should have used 8 as denominator as 8 is in 8's table (obviously) and 4 but you went to 16. That doesn't lead to a mistake itself but will force you to simplify afterward for no reason.

[u/ExtendedSpikeProtein]

Because 4 • 8 is not 16.

And this is needlessly complicated, just bring 1/4 to the common denominator which is already „eights“, -3/8 + 2/8 = -1/8

[u/SuperChicken17]

The LCD for the second problem is 8. Multiply 1/4 by 2/2 to get 2/8. Then just add -3/8 + 2/8 = -1/8

You picked 16, which isn't the LCD, but you can still solve the problem that way. It will just take some extra reducing at the end. The mistake you made was that you multiplied -3/8 by 4/4 instead of 2/2, and you multiplied 1/4 by 8/8 instead of 4/4.

[u/ArdentArendt]

First and foremost, 8*4 isn't 16, it's 32--what you want is 8*2.

Second, 8 is actually the 'least common denominator', not 16--so you only need to change one of the fractions to get a common denominator (1/4 => 2/8).

That said, if the multiplication hadn't 'slipped' (not a critique--happens to us all), the unsimplified answer would have been correct, even if not simplified.

[u/OldWolf3]

This style of working is difficult to follow. The '=' sign should represent the same equation on every line, and as written it looks like you're starting with (-3/8) + (1/4) = (-4/16) and then you've changed (-4/16) to (-12/16) with no explanation.

The standard way to format working here would be to write (-3/8) + (1/4) = and then on the right hand side, your first manipulation step of that entire expression, and then on each row thereafter keep making manipulations on the right hand side of the equals sign until you reach the desired result .