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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

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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