Question

the mean of the observation x, 2 X + 1, 2 X + 5 and 2 X + 9 is 30 what is the mean of the first three observation​

Answer 1

Answer:

Mean

Step-by-step explanation:

Mean = $\frac{sum of all given observations}{total number of observations}$

  ∴  30  =$\frac{x + 2x + 1 + 2x + 5 + 2x + 9}{4}$

  ∴   30 x 4  = 7x + 15

  ∴  120 = 7x + 15

  ∴  7x = 120 - 15

  ∴ 7x = 105

  ∴$x = \frac{105}{7}$

 ∴ x = 15

First three observations are;-

x = 15,

2x + 1 = 2(15) + 1 = 30 +1 = 31,

2x + 5 = 2(15) + 5 = 30 + 5 = 35

Now,

Mean of 15, 31 and 35 =$\frac{15 + 31 + 35}{3}$

                                        = $\frac{81}{3} = 27$

Ans:- 27

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Answer 2

Answer:

27

Step-by-step explanation:

(X+2X+1+2X+5+2X+9) /4  =30

(7X+15) /4=30

7X+15=120

X=15

No.s  are  15,31,35,39

mean of ist 3 obsvns is( 15+31+35) /3=27