The head circumference is measured for a sample of 17 girls

The head circumference is measured for a sample of 17 girls and a separate sample of 12 boys. the mean for the girls was 49 cm with a standard deviation of 1.25 cm. The mean for the boys was 50 cm with a mean standard deviation of 0.95 cm. What is the value of the pooled standard error for the difference in mean head circumference between girls and boys?

Answer key says 0.43 but I\'m not sure what equation they used

Solution

Value Pooled variance S^2= (n1-1*s1^2 + n2-1*s2^2 )/(n1+n2-2)
S^2 = (16*1.5625 + 11*0.9025) / (29- 2 )
S^2 = 1.2936

WHEN SD ARE NOT EQUAL              
SE = S * Sqrt ( 1 / n1 + 1 / n2 )              
Where,               
x1 = Mean of Sample 1, x2 = Mean of sample2              
sd1 = SD of Sample 1, sd2 = SD of sample2              
              
S^2 = 61.8173              
SE = S * Sqrt( 1 /29+ 1/26 )]              
= [ Sqrt(1.2936) * Sqrt( 1 /17+ 1/12 ) ]              
= 0.4288 ~ 0.43