Find all pairs of consecutive even positive integers, both of which are larger than 5 such that their sum is less than 23.


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Solution:
Let the two consecutive even positive integers be x and x + 2.
x > 5, x + 2 > 5, x + (x + 2) < 23

x > 5, x + 2 > 5 ⇒x > 5.
2x + 2 < 23
2x < 21
x < 21/2

i.e 21/2 > x > 5

Thus, the required pairs of consecutive odd positive integers are (6, 8) and (8, 10).

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Let x and x + 2 be the required pairs of consecutive even positive integers.

Given: x > 5 x + x + 2 < 23

⇒ 2x < 21

⇒ x < 10.5

∴ 5 < x < 10.5 x = 6, 8, 10

∴ Required possible pairs are (6, 8), (8, 10), (10,12)