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Question

In a locality, the houses are numbered in the following way: 

The house-numbers on one side of a road are consecutive odd integers starting from 301, while the house-numbers on the other side of the road are consecutive even numbers starting from 302. The total number of houses is the same on both sides of the road. 

If the difference of the sum of the house-numbers between the two sides of the road is 27, then the number of houses on each side of the road is

The correct answer is
27

House Numbering Setup

The problem describes house numbers on two sides of a road:

  • Side 1: Consecutive odd integers starting from 301 (301, 303, 305, ...).
  • Side 2: Consecutive even integers starting from 302 (302, 304, 306, ...).

Let '$n$' be the number of houses on each side. The total number of houses is the same on both sides.

Sum Calculation for Side 1 (Odd Numbers)

This is an arithmetic progression with:

  • First term, $a_1 = 301$.
  • Common difference, $d = 2$.
  • Number of terms = $n$.

The sum of an arithmetic series is given by $S_n = \frac{n}{2}[2a_1 + (n-1)d]$.

Sum for Side 1 ($S_{odd}$): $ S_{odd} = \frac{n}{2}[2(301) + (n-1)2] $ $ S_{odd} = \frac{n}{2}[602 + 2n - 2] $ $ S_{odd} = \frac{n}{2}[600 + 2n] $ $ S_{odd} = n(300 + n) = 300n + n^2 $

Sum Calculation for Side 2 (Even Numbers)

This is an arithmetic progression with:

  • First term, $b_1 = 302$.
  • Common difference, $d = 2$.
  • Number of terms = $n$.

Sum for Side 2 ($S_{even}$): $ S_{even} = \frac{n}{2}[2(302) + (n-1)2] $ $ S_{even} = \frac{n}{2}[604 + 2n - 2] $ $ S_{even} = \frac{n}{2}[602 + 2n] $ $ S_{even} = n(301 + n) = 301n + n^2 $

Difference Calculation

The difference between the sums is given as 27.

Difference $= S_{even} - S_{odd}$

$ (301n + n^2) - (300n + n^2) = 27 $ $ 301n + n^2 - 300n - n^2 = 27 $ $ n = 27 $

Conclusion

The number of houses on each side of the road is 27.

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Important Questions from Arithmetic Progression

  1. If the arithmetic mean of a, b, c is \(\rm \frac M 3\) and  \(\rm \frac{1}{a} + \frac{1}{b} = -\frac{1}{c} \) , then the arithmetic mean of a 2, b 2, c 2 is

  2. How many two-digit numbers are divisible by 3 ?

  3. A person saves Rs. 1000 more than he did the previous year. If he saves Rs. 2000 in the first year, in how many years will he save Rs. 170000?

  4. A car starts with a speed of 60 km/h with its speed increasing every one hour by 5 km/h. In how many hours will it cover 435 kms?

  5. How many natural numbers lie between 3 and 200 which are divisible by 7?

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