"A study was conducted to compare the costs of supporting a family of four Canadians for a year in different foreign cities. The lifestyle of living in Canada on an annual income of 75,000 dollars was the standard against which living in foreign cities was compared. A comparable living standard in Perth, Australia, and Mexico City was attained for about $64,000. Suppose an executive wants to determine whether there is any difference in the average annual cost of supporting her family of four in the manner to which they are accustomed in Perth and Mexico City. She uses the following data, randomly gathered from 11 families in each city, and an alpha of 0.01 to test this difference. She assumes the annual cost is normally distributed and the population variances are equal. What does the executive find?"
Perth, Australia 68600, 64700, 67500, 64700, 66700, 68000, 65000, 68600, 71000, 68500, 67500
Mexico 64000, 64000, 66400, 64900, 62000, 60500, 63200, 63000, 64500, 63500, 61800
H0 u1-u2=0 Ha u1-u2=/=0 n=11 a=0.01 xbar1=67345.4545 sample sd1=1955.1796011434 xbar2=63436.3636 sample sd2=1621.8956361448 t=xbar t=((x1-x2)/root((s1^2(n1-1))+(s2^2(n2-1))/n1+n2-2)*root((1/n1)+(1/n2)) -7280.7803/1486681.264/20*(root(22)/11=-0.35
The numerical answer is wrong so what mistake did I make? Whats the correct equation to solve for observed t.