CUET UG 2025 — General Test Arithmetic

A person is rowing a boat:

• With the stream (downstream) → Takes 30 minutes to go 10 km
• Against the stream (upstream) → Takes 40 minutes to return the same 10 km

When rowing a boat:

• Downstream (with stream) = Boat's speed + Stream's speed
• Upstream (against stream) = Boat's speed - Stream's speed

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Convert time to hours:

30 minutes $= \dfrac{30}{60} = 0.5$=6030​=0.5 hours

40 minutes $= \dfrac{40}{60} = \dfrac{2}{3}$=6040​=32​ hours

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Speed $= \dfrac{\text{Distance}}{\text{Time}}$=TimeDistance​

Downstream speed $= \dfrac{10}{0.5}$=0.510​

$= 20$=20 km/h

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Upstream speed $= \dfrac{10}{\frac{2}{3}}$=32​10​

$$= 10 \times \dfrac{3}{2}$$=10×23​

$= 15$=15 km/h

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Let:

• $b$b = boat's speed in still water
• $s$s = stream's speed

Downstream: $b + s = 20$b+s=20 ... (Equation 1)

Upstream: $b - s = 15$b−s=15 ... (Equation 2)

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Subtracting Equation 2 from Equation 1:

$$(b + s) - (b - s) = 20 - 15$$(b+s)−(b−s)=20−15

$$b + s - b + s = 5$$b+s−b+s=5

$$2s = 5$$2s=5

$s = 2.5$s=2.5 km/h

Therefore, the speed of the stream is 2.5 km/h.