If the mean and variance of eight numbers 3,7,9,12,13,20, x and y be 10 and 25 respectively, then x.y is equal to ________
3+7+9+12+13+20+x+y8=10
x+y=16
∑x2n−∑xn2=25
32+72+92+122+132+202+x2+y2=1000
x2+y2=148
xy=54