What is the sum of first 100 terms which are common to both the progressions? 17,21,25,... and 16,21,26,...
a)120000
b)100000
c)101111
d)101100
e)130000

• terms will be 1+20*1, 1+20*2, ...... 1+20*n where n = 100
  
  sum of first 100 such terms = 1+20*1+ 1+20*2 + ......+ 1+20*n
  = 100 +20*(1+2+....+100)= 100+20*101*100/2 = 100+1000*101 = 101100 .... option d)
• 13 years agoHelpfull: Yes(7) No(0)
• 17,21,25,29,33,37,41,45,49,53,57,61....(difference is 4)
  16,21,26,31,36,41,46,51,56,61,66,71......(difference is 5)
  from above 2 series the common terms are 21,41,61,.......(consider this as new series )
  as we can see they are A.P with common difference as 20
  by formula
  Sn=n/2(2*a+(n-1)d)
  a=first term of series, d= difference of terms,Sn= sum of n terms
  s100=100/2*(2*21+(100-1)20)
  =101100
• 6 years agoHelpfull: Yes(2) No(1)
• explain the ans briefly
• 10 years agoHelpfull: Yes(0) No(2)