Question

(e) In an arrangement of dots there are r rows. Each row contains 5 dots.​

Answer 1

The total number of dots are 221.

Step-by-step explanation:

Consider the provided information.

It is given that the total number of rows are 13. Each row is increased by 2 dots and first row has 5 dots.

We need to find the total number of dots.

Therefore, n=13, d=2, a=5, Sn=?

Use the formula: S_n=\frac{n}{2}[2a+(n-1)d]S

n

=

2

n

[2a+(n−1)d]

Substitute the respective values in the above formula.

S_n=\frac{13}{2}[2(5)+(13-1)2]S

n

=

2

13

[2(5)+(13−1)2]

S_n=\frac{13}{2}[10+24]S

n

=

2

13

[10+24]

S_n=\frac{13}{2}[34]S

n

=

2

13

[34]

S_n=13\times17S

n

=13×17

S_n=221S

n

=221

Hence, the total number of dots are 221.

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