The arithmetic mean of the four numbers is 6. The first three numbers are 3.9 6.1 and 7.8. find the fourth number.
| July 18, 2021 | education
The arithmetic mean of four numbers is by definition equal to their sum divided by 4.
Let us denote the required number by x.
Then (3.9 + 6.1 + 7.8 + x) / 4 = 6
Add the numbers on the left and multiply both sides by 4.
17.8 x = 24
Then x = 24 / 17.8 = 240/178 = 120/89 = 1 31/89
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