Number Series asked in RRB PO 2018 Prelims

Here are the number series asked in RRB PO 2018 prelims held on 12 August 2018. Find the missing number in the series

1. 5 , 4 , 7 , 20 , 79 , ?
   A) 208
   B) 394
   C) 102
   D) 103
   
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     Option B
   Explanation: *1-1,*2-1,*3-1,*4-1,*5-1
2. 3.9 , 5.5 , 8.7 , 13.5 , ?
   A) 20.2
   B) 18.3
   C) 19.9
   D) 21.5
   
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     Option C
   Explanation: difference of difference
   1.6  —— 3.2——4.8——6.4
   1.6——1.6——1.6
3. 220 , 224 , 208 , 272 , 16 , ?
   A) 1024
   B) 258
   C) 1040
   D) 278
   
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   Option C
   Explanation: +4 , -16, +64,-256,+1024
4. 800 , ? , 600 , 1500 , 5250
   A) 500
   B) 400
   C) 700
   D) 300
   
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   Option B
   Explanation: *0.5, *1.5,*2.5,*3.5