A rectangular board has a length of 15cm and width x cm. If its sides are doubled, find its new area.

Analyze the question: A rectangle has length 15 cm and width x cm. Each side is doubled, and we need the new area.

Concept: Area of a rectangle = length × width. If every side is doubled, each dimension is multiplied by 2, so the area is multiplied by 2 × 2 = 4.

Solution:

• Original area = 15 × x = 15x cm²
• New length = 2 × 15 = 30 cm
• New width = 2 × x = 2x cm
• New area = 30 × 2x = 60x cm²

Check: 4 × 15x = 60x, which agrees.

Answer: The new area is 60x cm², which is option A.

Tip: When all linear dimensions are scaled by a factor k, the area scales by k². Doubling gives 4 times the area, tripling gives 9 times. Many students wrongly just double the area (30x), which is option C, so be careful with that trap.