Answer :

To find: the sum of all integers between 84 and 719, which are multiples of 5.

Solution: 


The smallest and largest digits between 84 and 719 which are divisible by 5 is 85 and 715.

So the sequence will be 85,90,........... 715.

 a = 85, d = 5, l = 715


From the formula l=a+(n-1)d

The number of terms are: 

n = + 1


n= + 1


n=


n= 127


So there are 127 terms between 84 and 719.


Now to calculate the sum of 127 terms use the formula:


⇒ S127= (a + l)


⇒ S127= (85 + 715)


⇒ S127= (800) = 50800

So the sum of the terms between 84 and 719 is 50800.

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