Wow that's way too much. But I will do it because it is math and math is awesome :D
1) √27 * √50 ∕ √54 = 3√3 * 5√2 / 3√6 = 5
2) Hey are you kidding me the solution is fractional.
3) √-4 is imaginary
4) Weight required = \(640\times \dfrac{4}{4+3+3}=\mathbf{256kg}\)
5) 4x²+20x+3xy+15y = 4x(x + 5) + 3y(x + 5) = (4x + 3y)(x + 5)
6)
\(L = \dfrac{xh}{a(x+p)}\\ Lx + Lp = x\cdot(\dfrac{h}{a})\\ x(L-\dfrac{h}{a})=-Lp\\ x = \dfrac{-Lp}{L-\frac{h}{a}}=\mathbf{\dfrac{Lp}{h - aL}}\)
7) \(4:5 = \dfrac{4}{5}=0.8\)
8)
\(7\dfrac{3}{5}\times \dfrac{17}{19}\div\dfrac{15}{25}\\ =\dfrac{38}{5}\times \dfrac{17}{19}\times \dfrac{5}{3}\\ =\dfrac{34}{3}\\ =\mathbf{11\dfrac{1}{3}}\)
9) 5hrs/1 week and 2 days = 5hrs/9 days = 5hrs/216hrs = 5 : 216.
10) 3 1/2 - 2 7/12 = 3 6/12 - 2 7/12 = 11/12.
11) Negative square. <--- That's the definition.
12) LCM(14a²b²,7ab, 28ab²) = 28a²b².
13)
\(1\dfrac{1}{3}+\dfrac{2}{4}\times \dfrac{12}{16}-\dfrac{5}{6}\\ =\dfrac{4}{3}+\dfrac{1}{2}\times \dfrac{3}{4}-\dfrac{5}{6}\\ =\dfrac{4}{3}+\dfrac{3}{8}-\dfrac{5}{6}\\ =\dfrac{32}{24}+\dfrac{9}{24}-\dfrac{20}{24}\\ =\mathbf{\dfrac{7}{8}}\)
14)
\(\log_512.5-\log_52\\ =\log_5\dfrac{12.5}{2}\\ =\log_56.25\\ =\log_5\dfrac{25}{4}\\ =\log_525-\log_54\\ =\mathbf{2 - 2\log_52}\)
15) Working efficiency of each man = 245 hours per house per person.
Working efficiency of 12 men =245/12 hours per house = 20 hours 25 min. No answer like that....
16) required fraction = 1 - 1/5 - 2/5 = 2/5.
17) Selling price = 850 / (1 + 15%) * (1 + 20%) = 850 * 1.2 / 1.15 = 887 approximately.
18) 3/2
19) \(1\dfrac{6}{9}\times \dfrac{2}{3}-3\dfrac{1}{5}+2\dfrac{1}{2}\div\dfrac{1}{2}\\ =\dfrac{5}{3}\times \dfrac{2}{3}-\dfrac{16}{5}+5\\ =\dfrac{10}{9}-\dfrac{16}{5}+5\\ =\dfrac{50}{45}-\dfrac{144}{45}+\dfrac{225}{45}\\ =\dfrac{131}{45}\)
which is 2 41/45.
20) 16x⁵y⁴ * 48xy∕ 32xy* 24x3y2 = 576x8y6.