Question Details

Let  P k  represent the perimeter of a square with sides of length k . The value of the expression
P 1 + P 2 + P 3 + + P 10   is --------

Options

A

55

B

110

C

220

D

440

Show Answer

Correct Answer :

Option C

220

Solution :

The correct option is 220.

Let us break down the problem step-by-step to understand how to arrive at this answer.

First, we are given that Pk represents the perimeter of a square with sides of length k.

Recall that a square has four equal sides. The perimeter of a square with a side length of k is the sum of the lengths of all its four sides. Therefore, the formula for the perimeter is:
P k = 4 k

We need to find the value of the sum:
S = P 1 + P 2 + P 3 + + P 10

Substituting the perimeter formula Pk=4k into the expression, we get:
S = ( 4 × 1 ) + ( 4 × 2 ) + ( 4 × 3 ) + + ( 4 × 10 )

We can factor out the common constant multiplier, which is 4:
S = 4 × ( 1 + 2 + 3 + + 10 )

Now, we need to calculate the sum of the first 10 positive integers: 1+2+3++10.

Using the formula for the sum of the first n natural numbers, which is:
i = 1 n i = n ( n + 1 ) 2

For n=10, this calculation yields:
1 + 2 + 3 + + 10 = 10 × ( 10 + 1 ) 2 = 10 × 11 2 = 5 × 11 = 55

Substitute this sum back into our equation for S:
S = 4 × 55

Multiplying the terms, we get:
S = 220

Thus, the final value of the expression is 220.

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