Question

The mean of 1st 8 observations is 18 and last 8 observations is 20.If the mean of all 15 observations is 19.Find th 8th observations ​

Answer 1

Answer:

Step-by-step explanation:

Given mean of first 8 obs = 18

Then sum of first 8 obs = 18×8 = 144

Mean of last 8 obs = 20

Then sum of last 8 obs = 20×8 = 160

Let the 8th observation be x

Then 144 and 160 both have x

Sum of all 15 observations = 144+160 - x  [as there are 2 x s one in 144 and                                                                          the other in 160 only one x is                                                                              present in total observations]

Mean of all 15 observations is given as 19

⇒ (144 +160 -x)/15 = 19

⇒  304 - x = 19×15

⇒  304 - x = 285

⇒  -x = 285 -304

⇒  -x = -19

∴ x = 19

∴ The 8th observation is 19

Mark as brainliest please

Answer 2

Sum of 1st 8 observation = 8 × 18

= 144

Sum of last 8 observation = 8 × 20

= 160

Sum of the 15 observation = 15 × 19

= 285

8th observation =( 144 + 160 ) - 285

= 304 - 285

= 19