Question 969806
79.74  ANSWER

She has an average from 55 tests.  Two perfect tests will change the average but not much, because they are a small number compared to 55.  

The mean is the average of all the tests.

mean=total/number.

The total score is mean* number (multiply both sides of the equation by number).

79*55=total =4345

Two more tests, and the total has increased 200 (100 on each test).  It is now 4545.

The number of tests has increased 2, to 57.

The new average (or mean; the two words are the same)=4545/57 

79.74