72 is the minimum grade he must get on the last test in order to have an average of 77.
<u>Step-by-step explanation:</u>
The grades of a student are given 72,91,78,72 and the grade of his last test is not given.
- You have to find the minimum grade the student shall get, so that the student average must be 77.
- The four grades are already given. Therefore, we need to find only the fifth grade.
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.
