Question

find the sum of all multiples of 7 lying between 1 and 100​

Answer 1

Step-by-step explanation:

Step-by-step explanation:the first no after 100 divisible by 7 is 105 and last before 1000 is 994. n= ? From 994, n can be obtained. Thus, the answer is 70336.

Answer 2

Given,

Multiplies of seven lying between $1-100$

To find,

The sum of multiplies of seven lying between $1-100$ =?

Solution,

Multiples of seven lying between $1-100$ are given as,

$7,14,...,98$

We know,

$a_n=a+(n-1)d$

⇒ $98=7+(n-1)7$

⇒ $n=14$

Now finding the sum of fourteen terms.

We know,

$S_n=\frac{n}{2}[2a+(n-1)d]$

Now on putting the values we get,

⇒ $S_n=\frac{14}{2}[2\times7+(14-1)\times 7]$

⇒ $S_n=7[14+13\times7]$

⇒ $S_n=735$

So the sum of all multiples of seven lying between one and hundred is $735.$

Hence, the sem of all multiples of 7 lying between 1 and 100 is 735.