China · Ministry of Education (registration via CHSI) and admitting universities · pg · unverified source
National written papers in politics and a foreign language, plus mathematics (for engineering tracks) and a university-set specialty paper; followed by a university re-examination and interview.
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Official source: https://yz.chsi.com.cn/
Original questions written to this exam's published syllabus and pattern. Not past papers.
1. A well-mixed lake of volume 10⁷ m³ has an inflow and outflow of 10⁵ m³ per day. A pollutant enters at 0.2 mg L⁻¹ and decays with first-order rate 0.01 per day. What is the steady-state lake concentration?
C. 0.10 mg L⁻¹
τ = V/Q = 100 days; C = Cin/(1 + kτ) = 0.2/(1 + 1) = 0.10 mg L⁻¹. 0.074 is the plug-flow answer, Cin·e^(−kτ); 0.2 ignores decay; 0.40 multiplies by (1 + kτ) instead of dividing.
Environmental & Agro-ecosystem Modelling · Mass-balance and box models
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