Question

first coefficient of two groups has 100 items with mean 15 and s.d 3 .
whole group has 250 items with mean 15.6 and Q √13.44 .
find mean and S.D of second group ​

Answer 1

Answer:

Use σ

2

=

n

1

+n

2

n

1

×(σ

1

2

+d

1

2

)+n

2

×(σ

2

2

+d

2

2

)

where d

1

=m

1

−a

d

2

=m

2

−a

a= mean of the whole group.

Let m

2

= mean of the second group.

Therefore 15.6=

250

100×15+150×m

2

⇒ m

2

=

150

250×15.6−100×15

⇒ m

2

=

15

2400

m

2

=16

⇒ 13.44=

250

100×9+150×σ

2

+100×(0.6)

2

+150×(0.4)

2

⇒ σ=4. ans

Explanation:

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