SE of sum of 1971 sample scores = 14 x 40 = 560
SE of average of 1971 sample scores = (560/1600) x 100%
= 14/40 = 7/20 = 35/100
= .35
SE of sum of 1975 sample scores = same as 1971's = .35
(The box SD is bootstraped by the sample SD in both cases)
SE of the difference = the square root of (.35)^2 + (.35)^2
= .49
z = ( 1975 ave - 1971 ave - 0 )/ SE of difference
= (68.5 - 67.2)/.49 = 1.2/.49 = 2.6
The area under the normal curve from -2.6 to 2.6 is 99.07%, so the area to the right of 2.6 is .93/2 = .465%.
.465/100 = 4.65/1000
= 5/1000 (approx)
= 1/200