Question

. Find the sum of all natural numbers which are
multiples of 7 or 3 or both and lie between 200 and
500.​

Answer 1

Answer:

LCM of 3 and 7 is 21.....

now ....21×10=210>200

.....21×9=189<200

and 21×23=483<500

and 21×24=504≥500

and the aeries starts with

210,231,252,273,........,483

d=21

a=210

now ...483=210+(n-1)21

=>273+21=21n

=>294/21

=>n =14

now .....

s(14)=(0.5)×14×(210+483)=7×693=4851