- A35
- B20
- C40
- D55
Step-by-Step Solution
P = 2 × (l + b) → 70 = 2 × (l + 15) → l + 15 = 35 → l = 20 cm. Stopping at the half-perimeter gives 35; subtracting twice the breadth from the full perimeter (70 − 30) gives the trap 40.
Answer: B) 20
The perimeter of a rectangular photo frame is 70 cm and its breadth is 15 cm. Find its length (in cm).
Class 7Perimeter and AreaPerimeter and Area
Key idea: Parallelogram area
**Area of a parallelogram = base × height.**
Same idea as a rectangle, but the height is the perpendicular distance between the two parallel sides — NOT the slant length of the side. Pick any side as the base, drop a perpendicular to the opposite parallel side, measure that — that's the height.
Example: parallelogram with base 8 cm and perpendicular height 5 cm. Area = . The slant side could be longer; doesn't matter for area.
Perimeter of a parallelogram = 2 × (one side + adjacent side).
Same idea as a rectangle, but the height is the perpendicular distance between the two parallel sides — NOT the slant length of the side. Pick any side as the base, drop a perpendicular to the opposite parallel side, measure that — that's the height.
Example: parallelogram with base 8 cm and perpendicular height 5 cm. Area = . The slant side could be longer; doesn't matter for area.
Perimeter of a parallelogram = 2 × (one side + adjacent side).
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