Answer :
An average is written by the values / the amount of values.
We know there are 3 values, we know the numbers of 2, this can be modelled by the equation:
(78 + 85 + x)/3 = 85
We solve that ^:
(163+x)/3=85
163+x=255
x=92
The score on her 3rd test is 92
We know there are 3 values, we know the numbers of 2, this can be modelled by the equation:
(78 + 85 + x)/3 = 85
We solve that ^:
(163+x)/3=85
163+x=255
x=92
The score on her 3rd test is 92