Agent A is hired to test the destructiveness of the governments new M1 missile. Agent A tests 41 rockets, and by

Agent A is hired to test the destructiveness of the governments new M1 missile. Agent A tests 41 rockets, and by assuming normality, she calculates a 98% confidence interval their destructive force as (689,739.96). What was the average of Agent A's 41 rockets. 

My main question is can i just subtract the low end value of the interval from the high end value of the interval. Then divide the value i find by 2 to get the error value. Then add the error value to the low end to find the value. If i can do this value i calculated the mean to be 714.48. Or is this a trick question because the standard deviation was not given?