The mean of four numbers is 6. Three of them are 3.4,10.7and 7.8. what is the fourth number?

2.1

Step-by-step explanation:

Use the equation

Sum of elements = average x number of elements

sum = (6) (4)

sum = 24

Add up the numbers we know: 3.4 + 10.7 + 7.8 = 21.9

24 - 21.9 = 2.1

This means the fourth number is 2.1

2.1

Step-by-step explanation:

Let x be the 4th number. To find the mean add the 4 numbers and divide by 4

(3.4 + 10.7+7.8+x) / 4 = 6

Multiply each side by 4

(3.4 + 10.7+7.8+x) / 4 * 4 = 6*4

(3.4 + 10.7+7.8+x) = 24

Combine like terms

x+21.9=24

Subtract 21.9 from each side

x = 24-21.9

x = 2.1