Question

The average marks of 15 students is 45. If average marks of first 8 students is 48 and that of
last 8 students is 42, find the marks obtained by 8th student.

Answer 1

Answer:

Total marks of 48 students =48x45=2160

Let the number of boys be B and the number of girls be (48−B)

Then total marks of boys =40B

Total marks of girls =50(48−B)=2400−50B

⇒ 40B+2400−50B=2160

⇒ 10B=240

⇒ B=24

Thus number of girls =48−24=24

Therefore, required ratio =24:24=1:1

Step-by-step explanation:

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Answer 2

Answer:

The marks obtained by 8th number is 45.

Step-by-step explanation:

Given average marks of 15 students is 45.

So total sum of marks of 15 students is

$(45 \times 15) = 675$

Average marks of 1st 8 students is 48.

So total sum of marks of first 8 students is

$48 \times 8 = 384$

Average marks of last 8 students is 42.

So total sum of marks of last 8 students is

$8 \times 42 = 336$

Now 8 th number of student got mark

$(336 + 384) - 675 = 720 - 675 = 45$

Therefore the marks obtained by 8th number is 45.