Question 1132785
The total is average*n, so the total for 24 is 74*24=1776
the 25th students's score adds to 1776 to get 1840.  Now divide by 25 to get 73.60.  The average decreases.
The score for the last student's test is 10 fewer than the average, and still 9.6 fewer than the new average.  That will increase the standard deviation.