Question Details

The number of district pairs of integers (x, y) satisfying the inequalities x > y >= 3 and x + y < 14 is

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Correct Answer :

16

Solution :

The correct answer is 16.

We are given two inequalities involving integers x and y:

x>y3

x+y<14

Let's analyze the possible integer values for y starting from its minimum possible value, which is 3.

Case 1: Let y=3

Since x>y, we have x>3, which means x4.

Substitute y=3 into the second inequality:
x+3<14
x<11

Thus, x can take the integer values 4, 5, 6, 7, 8, 9, and 10. There are 7 pairs here.

Case 2: Let y=4

Since x>y, we have x>4, which means x5.

Substitute y=4 into the second inequality:
x+4<14
x<10

Thus, x can take the integer values 5, 6, 7, 8, and 9. There are 5 pairs here.

Case 3: Let y=5

Since x>y, we have x>5, which means x6.

Substitute y=5 into the second inequality:
x+5<14
x<9

Thus, x can take the integer values 6, 7, and 8. There are 3 pairs here.

Case 4: Let y=6

Since x>y, we have x>6, which means x7.

Substitute y=6 into the second inequality:
x+6<14
x<8

Thus, x can take the single integer value 7. There is 1 pair here.

Case 5: Let y=7

Since x>y, we have x8.

Substitute y=7 into the second inequality:
x+7<14
x<7

There is no integer x that is greater than or equal to 8 and strictly less than 7. Therefore, there are no pairs for y7.

To find the total number of distinct pairs, we add the valid possibilities from all the cases:

7+5+3+1=16

There are exactly 16 distinct integer pairs of (x,y) that satisfy the given inequalities.

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