15. A tank can fill by two taps X a...
Question

# 15. A tank can fill by two taps X and Y in 5 h and 10 h, respectively while another tap Z empties the tank in 20 h. In how many hours can the tank be filled if all 3 taps are kept open? RRB NTPC (Phase 1) 2016 (1) 5 (2) 4 (3) 7 (4) 8

11th - 12th Class
Maths
Solution
154
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15. (2) According to the question, [ begin{aligned} (x+y+z)^{prime} s 1 h w o r k &=frac{1}{5}+frac{1}{10}-frac{1}{20} &=frac{4+2-1}{20}=frac{5}{20}=frac{1}{4} end{aligned} ] Hence, total taken time ( =frac{1}{frac{1}{4}}=4 h )