answer:**Analysis** This question primarily examines the judgment of sufficient and necessary conditions, which is quite basic. One can judge based on the definitions of sufficient and necessary conditions. **Solution** Given a, b in mathbb{R}, then (a-b)a^2 < 0, it follows that a < b holds. From a < b, we have a-b < 0, and "(a-b)a^2 leqslant 0", thus, according to the definitions of sufficient and necessary conditions, we can judge: For a, b in mathbb{R}, the statement "(a-b)a^2 < 0" is a sufficient but not necessary condition for a < b. Therefore, the correct choice is boxed{text{A}}.

answer:Let's call the certain number "x". According to the given equation: 6 - x = 2 To find the value of x, we can solve for x by subtracting 6 from both sides of the equation: -x = 2 - 6 -x = -4 Now, to find the value of x, we multiply both sides by -1 to get rid of the negative sign: x = 4 Now, we need to find the value of the certain number (x) minus 2: x - 2 = 4 - 2 x - 2 = 2 So, the value of the certain number minus 2 is boxed{2} .

answer:1. **Calculate the current average score**: Josanna's current test scores are 90, 80, 70, 60, and 85. To find the average of these scores, sum them up and divide by the number of scores: [ text{Current Average} = frac{90 + 80 + 70 + 60 + 85}{5} = frac{385}{5} = 77 ] 2. **Determine the desired average score**: Josanna wants to raise her average by at least 3 points. Therefore, her target average score after the next test is: [ text{Target Average} = 77 + 3 = 80 ] 3. **Set up an equation for the sixth test score**: Let x be the score Josanna needs on her sixth test to achieve an average of 80. The total score after six tests would then be 385 + x. The average score after six tests should be 80, so we set up the equation: [ frac{385 + x}{6} = 80 ] 4. **Solve for x**: [ 385 + x = 80 times 6 ] [ 385 + x = 480 ] [ x = 480 - 385 = 95 ] 5. **Conclusion**: The minimum score Josanna needs on her sixth test to achieve her goal is boxed{95 textbf{(E)}}.

answer:If there are 30 questions worth two points each, then the total points from these questions is 30 * 2 = 60 points. Since the test is worth 100 points in total, we need to find out how many points are remaining after the 2-point questions. So, we subtract the points from the 2-point questions from the total points of the test: 100 points (total) - 60 points (from 2-point questions) = 40 points remaining. These remaining points must come from the 4-point questions. To find out how many 4-point questions there are, we divide the remaining points by the points per question: 40 points / 4 points per question = 10 questions. So, there are 10 questions worth four points each. To find the total number of questions on the test, we add the number of 2-point questions to the number of 4-point questions: 30 questions (2-point) + 10 questions (4-point) = boxed{40} questions in total.