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Page 1 RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Question 1. Solution: We know: Area of a triangle = 1/2×Base×Height (i) Base = 42 cm Height = 25 cm ? Area of the triangle = (1/2×42×25) cm 2 = 525 cm 2 (ii) Base = 16.8 m Height = 75 cm = 0.75 m [since 100 cm = 1 m] ? Area of the triangle = (1/2×16.8×0.75) m 2 = 6.3 m 2 (iii) Base = 8 dm = (8 × 10) cm = 80 cm [since 1 dm = 10 cm] Height = 35 cm ? Area of the triangle = (1/2×80×35) cm 2 = 1400 cm 2 Question 2. Solution: Base of triangle = 16 cm area of the triangle = 72 cm² Page 2 RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Question 1. Solution: We know: Area of a triangle = 1/2×Base×Height (i) Base = 42 cm Height = 25 cm ? Area of the triangle = (1/2×42×25) cm 2 = 525 cm 2 (ii) Base = 16.8 m Height = 75 cm = 0.75 m [since 100 cm = 1 m] ? Area of the triangle = (1/2×16.8×0.75) m 2 = 6.3 m 2 (iii) Base = 8 dm = (8 × 10) cm = 80 cm [since 1 dm = 10 cm] Height = 35 cm ? Area of the triangle = (1/2×80×35) cm 2 = 1400 cm 2 Question 2. Solution: Base of triangle = 16 cm area of the triangle = 72 cm² RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Question 3. Solution: Area of triangular region = 224 m² Base = 28 m Question 4. Solution: Area of triangle = 90 cm² and height (h) = 12 cm Question 5. Solution: Let height of a triangular field = x m Then base (b) = 3x m and area =1/2 bh = ½ x 3x x x Page 3 RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Question 1. Solution: We know: Area of a triangle = 1/2×Base×Height (i) Base = 42 cm Height = 25 cm ? Area of the triangle = (1/2×42×25) cm 2 = 525 cm 2 (ii) Base = 16.8 m Height = 75 cm = 0.75 m [since 100 cm = 1 m] ? Area of the triangle = (1/2×16.8×0.75) m 2 = 6.3 m 2 (iii) Base = 8 dm = (8 × 10) cm = 80 cm [since 1 dm = 10 cm] Height = 35 cm ? Area of the triangle = (1/2×80×35) cm 2 = 1400 cm 2 Question 2. Solution: Base of triangle = 16 cm area of the triangle = 72 cm² RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Question 3. Solution: Area of triangular region = 224 m² Base = 28 m Question 4. Solution: Area of triangle = 90 cm² and height (h) = 12 cm Question 5. Solution: Let height of a triangular field = x m Then base (b) = 3x m and area =1/2 bh = ½ x 3x x x RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Solution: Area of the right angled triangle = 129.5 cm² Question 7. Solution: In right angled ?ABC, Base BC = 1.2 m Question 6. Page 4 RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Question 1. Solution: We know: Area of a triangle = 1/2×Base×Height (i) Base = 42 cm Height = 25 cm ? Area of the triangle = (1/2×42×25) cm 2 = 525 cm 2 (ii) Base = 16.8 m Height = 75 cm = 0.75 m [since 100 cm = 1 m] ? Area of the triangle = (1/2×16.8×0.75) m 2 = 6.3 m 2 (iii) Base = 8 dm = (8 × 10) cm = 80 cm [since 1 dm = 10 cm] Height = 35 cm ? Area of the triangle = (1/2×80×35) cm 2 = 1400 cm 2 Question 2. Solution: Base of triangle = 16 cm area of the triangle = 72 cm² RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Question 3. Solution: Area of triangular region = 224 m² Base = 28 m Question 4. Solution: Area of triangle = 90 cm² and height (h) = 12 cm Question 5. Solution: Let height of a triangular field = x m Then base (b) = 3x m and area =1/2 bh = ½ x 3x x x RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Solution: Area of the right angled triangle = 129.5 cm² Question 7. Solution: In right angled ?ABC, Base BC = 1.2 m Question 6. RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D and hypotenuse AC = 3.7 m But AC² = AB² + BC² (Pythagoras Theorem) ? (3.7)² = AB² + (1.2)² ? 13.69 = AB² + 1.44 ? AB² = 13.69 – 1.44 ? AB² = 12.25 = (3.5)² ? AB = 3.5 m Now, area of ?ABC = ½ x base x altitude = ½ x 1.2 x 3.5 m² = 2.1 m² Question 8. Solution: Legs of a right angled triangle = 3 : 4 Let one leg (base) = 3x Then second leg (altitude) = 4x Area = ½ x base x altitude = ½ x 3x x 4x = 6x² 6x² = 1014 ? x² = 1014/6 = 169 = (13)² x = 13 one leg'(Base) = 3x = 3 x 13 = 39 cm and second leg (altitude) = 4x = 4 x 13 = 52 cm Page 5 RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Question 1. Solution: We know: Area of a triangle = 1/2×Base×Height (i) Base = 42 cm Height = 25 cm ? Area of the triangle = (1/2×42×25) cm 2 = 525 cm 2 (ii) Base = 16.8 m Height = 75 cm = 0.75 m [since 100 cm = 1 m] ? Area of the triangle = (1/2×16.8×0.75) m 2 = 6.3 m 2 (iii) Base = 8 dm = (8 × 10) cm = 80 cm [since 1 dm = 10 cm] Height = 35 cm ? Area of the triangle = (1/2×80×35) cm 2 = 1400 cm 2 Question 2. Solution: Base of triangle = 16 cm area of the triangle = 72 cm² RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Question 3. Solution: Area of triangular region = 224 m² Base = 28 m Question 4. Solution: Area of triangle = 90 cm² and height (h) = 12 cm Question 5. Solution: Let height of a triangular field = x m Then base (b) = 3x m and area =1/2 bh = ½ x 3x x x RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Solution: Area of the right angled triangle = 129.5 cm² Question 7. Solution: In right angled ?ABC, Base BC = 1.2 m Question 6. RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D and hypotenuse AC = 3.7 m But AC² = AB² + BC² (Pythagoras Theorem) ? (3.7)² = AB² + (1.2)² ? 13.69 = AB² + 1.44 ? AB² = 13.69 – 1.44 ? AB² = 12.25 = (3.5)² ? AB = 3.5 m Now, area of ?ABC = ½ x base x altitude = ½ x 1.2 x 3.5 m² = 2.1 m² Question 8. Solution: Legs of a right angled triangle = 3 : 4 Let one leg (base) = 3x Then second leg (altitude) = 4x Area = ½ x base x altitude = ½ x 3x x 4x = 6x² 6x² = 1014 ? x² = 1014/6 = 169 = (13)² x = 13 one leg'(Base) = 3x = 3 x 13 = 39 cm and second leg (altitude) = 4x = 4 x 13 = 52 cm RS Aggarwal Solutions Class 7 Chapter 20 - Mensuration (Ex 20D) Exercise 20D Question 9. Solution: One side BC of a right triangular scarf = 80 cm and longest side AC = 1 m = 100 cm By Pythagoras Theorem, AC² = AB² + BC² ? (100)² = AB² + (80)² ? 10000 = AB² + 6400 ? AB² = 10000 – 6400 ? AB² = 3600 = (60)² ? AB = 60 Second side = 60 cm Area of the scarf = ½ x b x h = ½ x 80 x 60 cm 2 = 2400 cm² Rate of cost = Rs. 250 per m² Total cost =2400/200 x 250 = Rs. 60Read More
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