<PRE><B>Question 1097743</B>
he has already scored 89 + 93 + 87


the sum of this is 269.


in order to average a 90, he needs to score a total of 4 * 90 = 360 on all 4 tests.


360 - 269 = 91.


he needs to score at least a 91 to get a 90 average on all 4 tests.


269 + 91 = 360


360 / 4 = 90


the general formula is sum of scores / number of tests = average score on each test.


from this formula, you can easily derive:


sum of scores = average score on each test * number of tests


when he gets a 91 on the last test, than the 4 individual scores are 89, 93, 87, 91.


add them up and you get a total of 360 for 4 scores.


average is 360 / 4 = 90.










</PRE>