21. If x+y+z=0,then x^{2}/yx + y^{2}/zx + z^{2}/xy equal

- Option : D
- Explanation : x
^{2}/yx + y^{2}/zx + z^{2}/xy

...(since, x+y+z=0 x^{3}+y^{3}+z^{3}=3xyz)

(x^{3}+y^{3}+z^{3}) / xyz = 3xyz / xyz = 3.

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- Option : B
- Explanation : Increase after 5 years should have been 7 x 5 = 35 years. But since average remains same, diference in their age is 35 years.

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24. What is the maximum sum of the series 60, 58, 56, 54, 52, ?

- Option : C
- Explanation :
Since d = -2, maximum sum of the series will be sum of all the positive terms.

Least positive term of the series is 2 or 0 (both giving equal sum)

Let, 2 be the n^{th}term

2 = 60 + (n 1) - 2

=> n = 30

Required sum = 30/2 (60 + 2) = 930

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- Option : D
- Explanation :
L.C.M. of 12, 21 and 35 = 420

∴ Number required = 420 + 6 = 426

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