Question

The mean of 7 observation is 20.If the mean of the first four observation is 18 and that of the last four is 22 .Find the fourth observation

Answer 1

7 observation
$7 \times 20 = 140$
1st 4 observation
$4 \times 18 = 72$

Last 4 observation
$22 \times 4 = 88$
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4th observation =
$(72 + 88) - 140 = 20$

Answer 2

Answer:

mean of 7observation is 20

so we need to multiply seven observation by 20

answer is140

first four observation is 18

we need to multiply by 4 and 18

answer 72

last four observation is 22

again we need to multiply by 4and 22

answer 88

since the fourth observation is twice

*the fourth observation equal to

77+88 -140 is 20

I hope this answer is correct