Seven students take a speed reading course in order to improve their reading ability. The reading scores of the seven before and after taking the course are given below:

person 1 2 3 4 5 6 7

x Test Score (before) 350 371 360 400 450 389 410

y Test Score (after) 370 366 365 413 440 420 419

Note thatn= 7. We will defined1= x1- y1. After doing the appropriate calculations, we find that .

d^- =-9 S_d = 14.12

Find the 80 % confidence interval for mean of the differences,d.