I'm quite bad with math but I'd really love to learn some statistics... I got stuck on the following :

They ask me :

1 This question refers to the table above. According to Column 2, what is the effect of tracking on test scores?

So the answer is : 0.175 (correct)

2 Use the same table as above. According to Column 3, what is the effect of tracking on test scores for students in the top half of the initial distribution?

I thought should be : 0.02 + (0.191-0.155) = 0.056

but I'm not sure and I have only one attempt

3 Use the same table as above. According to Column 3, what is the effect of tracking on test scores for students in the bottom half of the initial distribution?

I thought 0.155 + 0.036 ... which would be exactly 0.191..... sound's tricky and again I have only one attempts

Thanks a lot