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Four numbers whose sum is 40 and sum of their squares is 480. What are the four numbers?(a) 4, 8, 12, and -16(b) 4, 8, 12, and 16(c) -4, 8, 12, and 16(d) 4, -8, 12, and 16The question was asked during an online interview.Asked question is from Arithmetic Progression Basics in division Arithmetic Progressions of Mathematics – Class 10 |
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Answer» RIGHT choice is (b) 4, 8, 12, and 16 To elaborate: LET the four NUMBERS be (a + 3d), (a + d), (a – 3d), (a – d). Sum of the four numbers is 40. a + 3d + a + d + a – 3d + a – d = 40 4a = 40 a = 10 Sum of their SQUARES is 480. (a + 3d)^2 + (a + d)^2 + (a – 3d)^2 + (a – d)^2 = 480 4a^2 + 20d^2 = 480 10^2 + 5d^2 = 120 100 + 5d^2 = 120 5d^2 = 20 d^2 = 4 d = 2, -2 Hence the four numbers are 4, 8, 12, and 16. |
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