Question
The speed of a plane was raised by 60% by the pilot and
then the raised speed was reduced by 50%. The speed measured by the sonic radar at this point of time was 2400 km/h. Find the initial speed of the plane.Solution
Let, the initial speed = x km/hr Speed after increasing = x + [x × (60/100)] = x + (3x/5) = 8x/5 km/hr Speed after decreasing = (8x/5) – [(8x/5) × (50/100)] => (8x/5) - (4x/5) = 8x - (4x/5) = 4x/5 km/hr According to the data mentioned in the question, => 4x/5 = 2400 => x = 2400 × (5/4) => x = 3000 ∴ The initial speed was 3000 km/hr.
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