Arithmetic Progression

In a potato race, a bucket is placed at the starting point, which is 5 m from the first potato and other potatoes are placed 3 m apart in a straight line. There are ten potatoes in the line. A competitor starts from the bucket, picks up the nearest potato, runs back with it, drops it in the bucket, runs back to pick up the next potato, runs to the bucket to drop it in, and she continues in the same way until all the potatoes are in the bucket. What is the total distance the competitor has to run?
[Hint: to pick up the first potato and the second potato, the total distance (in metres) run by a competitor is 2×5+2×(5+3)]

Solution: The distances between the bucket and the potatoes are 5, 8, 11, 14,..., which is in the form of AP. Given that the competitor's journey for gathering these potatoes is two times the...

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A spiral is made up of successive semicircles, with centres alternately at A and B, starting with centre at A of radii 0.5, 1.0 cm, 1.5 cm, 2.0 cm, ……… as shown in figure. What is the total length of such a spiral made up of thirteen consecutive semicircles? (Take π = 22/7)

Solution: We are aware that, The perimeter of a semi-circle is πr Therefore, P1 = π(0.5) = π/2 cm P2 = π(1) = π cm P3 = π(1.5) = 3π/2 cm We can say that, P1, P2, P3 are...

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In a school, students thought of planting trees in and around the school to reduce air pollution. It was decided that the number of trees, that each section of each class will plant, will be the same as the class, in which they are studying, e.g., a section of class I will plant 1 tree, a section of class II will plant 2 trees and so on till class XII. There are three sections of each class. How many trees will be planted by the students?

Solution: It is clear that the number of trees planted by students is in the form of A.P. 1, 2, 3, 4, 5………………..12 The first term, a = 1 The common difference, d = 2−1 = 1...

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A contract on construction job specifies a penalty for delay of completion beyond a certain date as follows: Rs. 200 for the first day, Rs. 250 for the second day, Rs. 300 for the third day, etc., the penalty for each succeeding day being Rs. 50 more than for the preceding day. How much money the contractor has to pay as penalty, if he has delayed the work by 30 days.

Solution: The given penalties are in the form of an A.P. having the first term as 200 and the common difference as 50, as can be seen. As a result, a = 200...

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A small terrace at a football ground comprises of 15 steps each of which is 50 m long and built of solid concrete. Each step has a rise of 1 4 m and a tread of 1 2 m. (see Fig. 5.8)Calculate the total volume of concrete required to build the terrace. [Hint : Volume of concrete required to build the first step = ¼ ×1/2 ×50 m3.]

Solution: The first step is $\frac{1}{2}$ m wide, the second step is 1 m wide, and the third step is $\frac{3}{2}$m wide, as seen in the diagram. When the height reaches $\frac{1}{4}$ m, we can see...

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The houses of a row are numbered consecutively from 1 to 49. Show that there is a value of x such that the sum of the numbers of the houses preceding the house numbered x is equal to the sum of the numbers of the houses following it. Find this value of x. [Hint :Sx – 1 = S49 – Sx ]

Solution: Given, Row houses have numbers ranging from 1,2,3,4,5,......49. As a result, we can observe that the houses in a row are in the form of AP. So, The first term, a = 1 The common difference,...

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A ladder has rungs 25 cm apart. (see Fig. 5.7). The rungs decrease uniformly in length from 45 cm at the bottom to 25 cm at the top. If the top and the bottom rungs are apart, what is the length of the wood required for the rungs? [Hint: Number of rungs = -250/25 ].

Solution: Given, The ladder has a 25cm distance between the rungs. The distance between the ladder's top and bottom rungs of ladder is $=2\frac{1}{2}m=2\frac{1}{2}*100cm$= 5/2 ×100cm = 250cm As a...

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