Question

A small terrace at a football ground comprises of 15 steps each of which is 50m long and built of solid concrete. Each step has a rise of 1/4 m and a tread of 1/2m. Calculate the total volume of concrete required to build the terrace. ​

Answer 1

Answer:

A small terrace at a football ground comprises of 15 steps each of which is 50m long and built of solid concrete. Each step has a rise of 1/4 m and a tread of 1/2m. Calculate the total volume of concrete required to build the terrace.

Explanation:

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myself Samriddhi

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Answer 2

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 ¼ m and a tread of ½ 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 × ½ × 50 m3]

Solution:

The sum of the first n terms of an AP is given by Sₙ = n/2 [2a + (n - 1) d], where a is the first term, d is a common difference and n is the number of terms.

From the figure, it can be observed that the Height of 1st step is ¼ m

Height of the 2nd step is (¼ + ¼) m = ½ m

Height of 3rd step is (¼ + ¼ + ¼) m = 3/4 m

Therefore, the height of each step is increasing by ¼ m

Length 50m and width (tread) is the same for each step that is ½ m

Volume of step can be considered as Volume of Cuboid = length × breadth × height

Volume of concrete in 1st step = 50m × ½ m × ¼ m = 6.25 m³

Volume of concrete in 2nd step = 50m × ½ m × ½ m = 12.50 m3

Volume of concrete in 3rd step = 50m × ½ m × ¾ m = 18.75 m3

It can be observed that the volumes of concrete in these steps are in an A.P.: 6.25m³, 12.50m³, 18.75m³, ....

First term a = 6.25, Common difference d = 6.25

Let nth term of AP be the 15th value since number of steps = 15

Sum of n terms, Sₙ = n/2 [2a + (n - 1) d]

S₁₅ = 15 / 2 [2 × 6.25 + (15 - 1) × 6.25]

= 15 / 2 [12.50 + 14 × 6.25]

= 15 / 2 [12.50 + 87.50]

= 15/2 × 100

= 750 m³

Therefore, the volume of concrete required to build the terrace is 750 m³.

Explanation:

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