(1) Find the probability (given reason for formula you use) of what a number is selected at random from 1000 to 9999, and the sum of the digits of the number is exactly 9. (10%)

2. In the region just downstream of a sluice gate, the water may develop a reverse flow region as is in Fig-1. The velocity profile is assumed to consist of two uniform regions, one with velocity Va =3 m/s and the other with Vb =0.9 m/s. Determine the net flowrate of water across the portion of the control surface at section (2) if the channel is 6 m wide. (20%)

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(1) Find the probability (given reason for formula you use) of what a number is selected at random from 1000 to 9999, and the sum of the digits of the number is exactly 9. (10%)

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