A student has gotten the following grades on his tests. What is the minimum grade he must get on the last test in order to have an average of 77?
72 ,91 ,78, 72
The minimum grade he must get on the last test in order to have an average of 77 is
(Simplify your answer.)

72 is the minimum grade he must get on the last test in order to have an average of 77.

Step-by-step explanation:

The grades of a student are given 72,91,78,72 and the grade of his last test is not given.

The term average is defined as the sum of all the data in a set divided by the number of data in a set.

Here, the number of data is 5. (Because the students has 4 grades plus one grade for his last test).

The average he should get is 77.

Average = Sum of all grades / number of grades

Let, 'x' be the grade of the last test.

⇒ 77 = (72+91+78+72+x) / 5

⇒ 77 = (313+x) / 5

⇒ 385 = 313 + x

⇒ x = 385 - 313

⇒ x = 72

The minimum grade he must get on the last test is 72.

1/5^2 = 7.56/45