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Statistics

Question
CBSEENMA9003285

A field is in the shape of a trapezium whose parallel sides are 25 m and 10 m. The non-parallel sides are 14 m and 13 m. Find the area of the field.

Solution

Let the given field be in the shape of a trapezium ABCD in which AB = 25 m, CD = 10 m, BC = 13 m and AD = 14 m.
From D, draw DE || BC meeting AB at E. Also, draw DF ⊥ AB.
∴ DE = BC = 13 m
AE = AB – EB = AB – DC
= 25 – 10= 15 m

For ΔAED
a = 14 m b = 13 m c = 15 m
therefore space space space space straight s equals fraction numerator straight a plus straight b plus straight c over denominator 2 end fraction equals fraction numerator 14 plus 13 plus 15 over denominator 2 end fraction equals 42 over 2 equals 21 space straight m
∴ Area of the ΔAED
             equals square root of straight s left parenthesis straight s minus straight a right parenthesis left parenthesis straight s minus straight b right parenthesis left parenthesis straight s minus straight c right parenthesis end root
equals square root of 21 left parenthesis 21 minus 14 right parenthesis left parenthesis 21 minus 13 right parenthesis left parenthesis 21 minus 15 right parenthesis end root
equals space square root of 21 left parenthesis 7 right parenthesis left parenthesis 8 right parenthesis left parenthesis 6 right parenthesis end root
equals square root of left parenthesis 7 cross times 3 right parenthesis left parenthesis 7 right parenthesis left parenthesis 4 cross times 2 right parenthesis left parenthesis 2 cross times 3 right parenthesis end root
equals 7 cross times 3 cross times 2 cross times 2 equals 84 space space straight m squared
rightwards double arrow space space space 1 half cross times AE cross times DE equals 84
rightwards double arrow space space space 1 half cross times 15 cross times DF equals 84
rightwards double arrow space space space space DF equals fraction numerator 84 cross times 2 over denominator 15 end fraction
rightwards double arrow space space space space DF equals 56 over 5 space straight m space equals space 11.2 space straight m
⇒ Height of the trapezium is 11.2 m. ∴ Area of parallelogram EBCD = Base x Height
equals space EB cross times DF equals 10 cross times 56 over 5 equals 112 space straight m squared

Area of the field = Area of ∴AED + Area of parallelogram EBCD
= 84 m2 + 112 m2 = 196 m2.

 

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