SSC CGL 2025 Tier-I · 15 September 2025, Shift 2 · Quantitative Aptitude · Question 19 of 100

We transcribed this text from the pictures on a candidate's response sheet for this shift; the answer is the key SSC colour-marked on that sheet. Solution last reviewed 11 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. From 2025 the candidate response sheet prints every question and option as a picture, so the text here is transcribed from those pictures for this shift and checked against them independently; where the layout carries meaning, the picture is shown as well. Each answer is the key SSC colour-marked on that sheet. SSC released a tentative key for challenge and later its final one, both only to candidates behind a login, and the sheet does not say which of the two it carries. The solutions are written by UnlockIAS.

If the lateral surface area of a prism is 240 cm² and height is 8 cm, what is the perimeter of the base?

(a)30 cm
(b)24 cm
(c)36 cm
(d)40 cm

Answer

Why

Correct — A. The side faces of a right prism unroll into one rectangle, base perimeter × height.

Lateral surface area = P × h
240 = P × 8
Divide both sides by 8: P = 240 ÷ 8 = 30 cm

Perimeter of the base = 30 cm → option (a)

Why the others are wrong

(b)
24 cm — 24 cm × 8 cm = 192 cm², which is 48 cm² short of the 240 cm² lateral area the question gives.
(c)
36 cm — 36 cm × 8 cm = 288 cm², 48 cm² more than the given 240 cm². The perimeter must multiply by 8 to give exactly 240.
(d)
40 cm — 40 cm × 8 cm = 320 cm², a third more than 240 cm². A 30 cm perimeter times the 8 cm height is what makes 240.

Concept

Cut a right prism's side faces along one vertical edge and flatten them. They form one rectangle: its length is the sides of the base laid end to end — the perimeter — and its height is the prism's height.

So lateral surface area = perimeter × height, whatever the base shape. The base area enters only the total surface area and the volume.

The formula is for a right prism, whose side faces are rectangles standing upright on the base. The question says only "a prism"; the key reads it as a right prism.

Key facts

Lateral surface area of a right prism = perimeter of base × height.
Total surface area of a right prism = lateral surface area + 2 × base area.
Volume of a right prism = base area × height.
A cylinder's curved surface area, 2πr × h, is the same rule: base circumference × height.

Study next

Total surface area of a triangular or hexagonal prismVolume of a prism from its base area and heightCurved surface area of a cylinder, 2πrh, read as circumference × height

Common traps

Treating 240 cm² as the total surface area, which also counts the two bases.
Reaching for the base area, which belongs to the volume formula, not the lateral area.

The cylinder version is at 12 Sep 2024, 09:00, Quant Q.14: a lateral area of 1760 cm² over a 20 cm height gives a base circumference of 88 cm, so r = 14 cm and the volume is 12320 cm³.

21 Sep 2025, 16:00, Quant Q.14 uses the volume rule: a square-base prism of 1024 cm³ and height 16 cm has base area 64 cm² and side 8 cm.

Related PYQs

No directly related past PYQ was found.

Topic: Right Prism, Right Circular Cone, Right Circular Cylinder, Sphere, Hemispheres, Rectangular Parallelepiped, Regular Right Pyramid with triangular or square base — all 51 SSC CGL questions on it, every solved shift.