SSC CHSL 13 Apr 2021 Shift 3 Paper

Section: Quantitative Aptitude

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Question : 73 of 100

Marks: +1, -0

The average of the numbers

a, b, c

and

d

is

2 d+4

. Also, the average of the numbers

a

and

b; b

and

c; c

and

d

are 8,5 and 4 respectively. If

e=a+d+1

, then what is the average of the numbers

d

and

e

?

8
$8.5$
3
7

Solution:

Given,

\;{a+b+c+d}/{4}=2 d+4

⇒ \;\; a+b+c+d=8 d+16

⇒ \;\; a+b+c+d-8 d=16

⇒ \;\; a+b+c-7 d=16

. . . (i)
Now,

\;{a+b}/{2}=8 ⇒ a+b=16

. . . (ii)

\;{b+c}/{2}=5 ⇒ b+c=10

. . . (iii)
and

\;{c+d}/{2}=4 ⇒ c+d=8

. . . (iv)
From Eqs. (i), (ii) and (iv)

16+8 \;\; -d-7 d=16

8 d \;\; =24-16=8

d \;\; =1

Now, from Eqs. (i) and (iii);

a+10-7 × 1=16

⇒ \;\; a=16-3=13

\;\text " Now, e "\;=a+d+1

\;\; =13+1+1=15

∴ \;\text " Average of "\; d \;\text " and "\; e=\;{d+e}/{2}

\;\; =\;{1+15}/{2}=\;{16}/{2}=8

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