Question

Average of 9 observation is 87.average of first 5 is 79 and the next three is 92 find the 9th observation

Answer 1

sum of all observations = 9×87
= 783
sum of first five observations = 5×79 = 395
sum of nxt three observations = 3×92= 276
395+276= 671
9th observation = 783- 671 = 112

Answer 2

The 9th observation = 112

Given :

• Average of 9 observation is 87.
• Average of first 5 is 79 and the next three is 92

To find :

The 9th observation

Solution :

Step 1 of 3 :

Find sum of 9 observations

Here it is given that average of 9 observation is 87

So the sum of 9 observations

= 9 × 87

= 783

Step 2 of 3 :

Find sum of 8 observations

It is given that average of first 5 is 79 and the next three is 92

So the sum of 8 observations

= ( 5 × 79 ) + ( 3 × 92 )

= 395 + 276

= 671

Step 3 of 3 :

Find 9th observation

Hence 9th observation

= Sum of 9 observations - Sum of 8 observations

= 783 - 671

= 112

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