The number of district pairs of integers (x, y) satisfying the inequalities x > y >= 3 and x + y < 14 is
Correct Answer :
Solution :
The correct answer is 16.
We are given two inequalities involving integers and :
Let's analyze the possible integer values for starting from its minimum possible value, which is 3.
Case 1: Let
Since , we have , which means .
Substitute into the second inequality:
Thus, can take the integer values 4, 5, 6, 7, 8, 9, and 10. There are 7 pairs here.
Case 2: Let
Since , we have , which means .
Substitute into the second inequality:
Thus, can take the integer values 5, 6, 7, 8, and 9. There are 5 pairs here.
Case 3: Let
Since , we have , which means .
Substitute into the second inequality:
Thus, can take the integer values 6, 7, and 8. There are 3 pairs here.
Case 4: Let
Since , we have , which means .
Substitute into the second inequality:
Thus, can take the single integer value 7. There is 1 pair here.
Case 5: Let
Since , we have .
Substitute into the second inequality:
There is no integer that is greater than or equal to 8 and strictly less than 7. Therefore, there are no pairs for .
To find the total number of distinct pairs, we add the valid possibilities from all the cases:
There are exactly 16 distinct integer pairs of that satisfy the given inequalities.
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