GATE Questions

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Let initial thickness of the paper be 'T'
after first fold it will be '2T' = 21T
after second fold it will be '4T' = 22T 
after 50th fold it will be T x (250T)

The HF band is based on frequencies 3 to 30 Mhz. AM radio stations are in the HF band but normally are stated in kilohertz.

The four most common soil erosion prevention methods are vegetation, geotextiles, mulch, and retaining walls.

By planting grass in areas of concentrated water flow, farmers can prevent much of the soil erosion that results from runoff, as the grass stabilizes the soil while still providing an outlet for drainage.

Preventing soil erosion is critical in protecting your property and exposed soil, whether from wind, weather, running water, and even the after-effects of the forest fire.

A square and a rectangle each have 4 right (90 deg) angles. 

Both square and rctangle have 4 sides and 4 angles, but the only difference is square is a rectangle with all sides equal.

Active voice is used when the subject performs the action stated by the verb.

Metamorphism is the change of minerals or geologic texture in pre-existing rocks, without the protolith melting into liquid magma. The change occurs primarily due to heat, pressure, and the introduction of chemically active fluids.

The parent rock must be in solid form. Tons of pressure must be applied for metamorphism to happen. The process must take place underground.

River Congo is the only river which crosses the equator twice.

Any number which can be expressed as a fraction of two integers like P & Q as P/Q where Q is not equal to zero.

Every integer is a rational number since Q can be 1.

Hence, in the given options, 4 can be expressed as a simple fraction as 4/1. And all other options cannot be expressed as fractions.

Hence, 4 is a rational number in the given options.