Question

The average of four numbers is 20. If three numbers are 18, 19 and 15. What is the fourth number?​

Answer 1

Answer:

Let the unknown term = x

Average = Sum of terms / No. of terms

20 = (15 + 18 + 19 + x) / 4

20 × 4 = 52 + x

80 = 52 + x

80 - 52 = x

x = 28

So, the 4th term is 28

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Answer 2

Answer:

-26 is the answer.

Step-by-step explanation:

Let the fourth number be 'x'

The numbers are 18, 19, 15 and x

Average

$average = \frac{sum \: of \: the \: values}{number \: of \: values}$

$average = \frac{18 + 19 + 15 + x}{4} \\ = \frac{52 + x}{4}\\= \frac{52}{4} + \frac{x}{4} \\ = 13 + \frac{x}{4}$

Let

$13 + \frac{x}{2} = 0$

$= > \frac{x}{2} = 0 - 13 \\ = > x = - 13 \times 2 \\ = > x = - 26$

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