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If, in a pair of consecutive positive integers, both numbers are greater than 5 and their sum is less than 23, then the number of such pairs are:

Solution

Correct Option: 4

Let the consecutive positive integers be nn and n+1n+1, where nn is the smaller number.

Both numbers must be greater than 5:

n>5n > 5

n+1>5n + 1 > 5

The second condition is automatically satisfied if n>5n > 5.


The sum must be less than 23:

n+(n+1)<23n + (n + 1) < 23

2n+1<232n + 1 < 23

2n<222n < 22

n<11n < 11


Combining the conditions:

5<n<115 < n < 11

Since nn must be a positive integer, the possible values are:

n=6,7,8,9,10n = 6, 7, 8, 9, 10


The valid pairs are:

(6,7)(6, 7) with sum 1313

(7,8)(7, 8) with sum 1515

(8,9)(8, 9) with sum 1717

(9,10)(9, 10) with sum 1919

(10,11)(10, 11) with sum 2121


Therefore, there are 5 such pairs.

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