Out of seven given numbers, the average of the first four nu

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RRB ASM Exam (Ajmer) 2007 click here to view all questions

Out of seven given numbers, the average of the first four numbers is 4 and that of the last four numbers is also 4. If the average of all the seven numbers is 3, fourth number is

A3

B4

C7

D11

Nithin K ? Nov 20 '2016 at 19:20

Answer is : 11

Explanation :

Since the average of first four numbers is 4, 
the sum of first four numbers is 4*4 = 16
a1 + a2 + a3 + a4 =16 ..................(i)

Since the average of the last four numbers is 4, 
the sum of the last four numbers is 4*4 = 16
a4 + a5 + a6 + a7 = 16...................(ii)

Add (i) and (ii) and re-group. You will get
(a1 + a2 + a3 + a4 + a5 + a6 + a7) + a4 = 32 .......(iii)

Since the average of the seven numbers is 3, their sum is 3*7 = 21
Apply This Sum in eqation (iii)

we get,
21 + a4 = 32
a4 = 32 - 21
a4 = 11

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Answer is : 11 Explanation : Since the average of first four numbers is 4,  the sum of first four numbers is 4*4 = 16 a1 + a2 + a3 + a4 =16 ..................(i) Since the average of the last four numbers is 4,  the sum of the last four numbers is 4*4 = 16 a4 + a5 + a6 + a7 = 16...................(ii) Add (i) and (ii) and re-group. You will get (a1 + a2 + a3 + a4 + a5 + a6 + a7) + a4 = 32 .......(iii) Since the average of the seven numbers is 3, their sum is 3*7 = 21 Apply This Sum in eqation (iii) we get, 21 + a4 = 32 a4 = 32 - 21 a4 = 11 Nithin K ? answered Nov 20 '2016 at 19:20 All Comments

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