What is the sum of all +ve integers lying between 200 & 400 that are multiples of 7 ?

a)8729
b)8700
c)8428
d)8278

• to find number of numbers between 200 to 400 that are multiples of 7 use the formula
  tn=a+(n-1)d
  399=203+(n-1)7
  n=29
  
  to find sum of 29 numbers that are multiples of 7 is Sn=n(a+tn)/2=29(203+399)/2=8729
  
• 10 years agoHelpfull: Yes(3) No(0)
• a) 8729
  Numbers multiple of 7 are 203,210,....,399
  If n=number of terms with difference 7,then 399=203+(n-1)7 or n=29
  Sum of these terms=(29/2)(2*203+28*7)=8729
• 10 years agoHelpfull: Yes(0) No(0)
• first term is 203 and last is 399 so use A.P tn =a+(n-1)d find n=29 here d=7 because multiple of 7.. sn= n/2(a+(n-1)d) find sn= 8729
• 10 years agoHelpfull: Yes(0) No(0)
• ans is 8729 because series will start from 203 t0 399 total element is 29 so formula s=n/2{2a+(n-1)d}
  n 29 a=203 and d is 7
• 10 years agoHelpfull: Yes(0) No(0)