You compare the happiness of people forced to smile with those of people forced to frown. Both groups have the same number of participants. The mean happiness level in the smile group is 20. The mean happiness level in the frown group is 19. The standard deviation of both groups is 20. The effect size is:

0.05

Step-by-step explanation:

The Effect size  = (Difference in Means) / (Standard deviation)

= (20 - 19) / 20

= 1/20

= 0.05

for finding the midpoint of any given 2 pair of points simply add the respective x coordinates with other x coordinate and the y coordinate with other y coordinate and divide them by 2

in your question it will be :

(3+1)/2 for the x coordinate of mid point i.e 2

[8+(-4)]/2 for the y coordinate of midpoint i.e 2

so coordinates of mid point of points (3,8) and (1,-4) will be (2,2)