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

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Step-by-step explanation:

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