answer:To calculate Gondor's total earnings, we need to consider his earnings from both phone and laptop repairs separately and then sum them up. First, let's calculate the total earnings from phone repairs: - On Monday, he repaired 3 phones, and on Tuesday, he repaired 5 phones. So, the total number of phones repaired is 3 + 5 = 8 phones. - Since he earns 10 from repairing a phone, his total earnings from phone repairs are 10 times 8 = 80. Next, we calculate the total earnings from laptop repairs: - On Wednesday, he repaired 2 laptops, and on Thursday, he repaired 4 laptops. Thus, the total number of laptops repaired is 2 + 4 = 6 laptops. - Given that he earns 20 from repairing a laptop, his total earnings from laptop repairs are 20 times 6 = 120. Finally, to find Gondor's total earnings, we add his earnings from phone repairs and laptop repairs: - Total earnings = Earnings from phones + Earnings from laptops = 80 + 120 = 200. Therefore, Gondor's total earnings are boxed{200}.

answer:Given the equations m-n=-2 and mn=3, we are asked to find the value of the algebraic expression -m^{3}n+2m^{2}n^{2}-mn^{3}. Starting with the given expression: begin{align*} -m^{3}n+2m^{2}n^{2}-mn^{3} &= -mn(m^{2}-2mn+n^{2}) &= -mnleft(m-nright)^{2} &= -mnleft(-2right)^{2} &= -mn times 4 &= -3 times 4 &= -12. end{align*} Therefore, the value of the algebraic expression is boxed{-12}.

answer:Since the random variable xi follows a normal distribution N(50,sigma^{2}), the axis of symmetry of the normal curve is at x=50. Given that P(xi < 40)=0.3, it follows that P(xi > 60)=0.3, therefore, P(40 < xi < 60)=1-(0.3+0.3)=0.4. Hence, the answer is boxed{0.4}. Based on the fact that the random variable xi follows a normal distribution, knowing the axis of symmetry of the normal curve is at x=50, and given P(xi < 40)=0.3, to find P(40 < xi < 60), one only needs to rely on the symmetry of the normal distribution to obtain the answer. This question mainly examines the characteristics of the normal distribution curve and the meaning represented by the curve, the application of symmetry in function graphs, and other basic knowledge. It tests computational and problem-solving skills, and the integration of mathematical and geometric thinking, simplification, and transformation ideas. It is a basic question.

answer:In the equation C=2pi R, we analyze the components as follows: - 2 and pi are constants because their values do not change regardless of the situation. - R is considered the independent variable because it can be chosen freely. The value of R determines the outcome of other variables in the equation. - C, which represents the circumference of a circle, changes as R changes. This makes C the dependent variable because its value depends on the value chosen for R. Given these points, we can conclude that: - C is the dependent variable because its value depends on the value of R. - R is the independent variable because its value can be chosen freely and it influences the value of C. - 2 and pi are constants because their values remain the same regardless of the values of C and R. Therefore, the correct statement that describes the relationship between these variables in the circumference formula of a circle is: boxed{text{B: }Ctext{ is the dependent variable, }Rtext{ is the independent variable, }2text{, }pi text{ are constants}}.