# GMAT 700 800 Quant Question 18

#### Geometry | Coordinate Geometry & Permutation Combination

The given question is a challenging GMAT 700 800 level quant problem solving question combining concepts in coordinate geometry and permutation combination. A very interesting and challenging GMAT hard math question.

Question 18: Rectangle ABCD is constructed in the xy-plane so that sides AB and CD are parallel to the x-axis. Both the x and y coordinates of all four vertices of the rectangle are integers. How many rectangles can be constructed if x and y coordinates satisfy the inequality 11 < x < 29 and 5 ≤ y ≤ 13?

1. 153
2. 153C4
3. 4896
4. 2448
5. 5508

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### Explanatory Answer | GMAT Geometry Practice

#### KeyData

Sides AB and CD are parallel to x-axis.
So, AD and BC will be parallel to y-axis.

The x-coordinates take values from 12 to 28.
We can draw lines parallel to y-axis corresponding to each of these values.
So, we will be able to draw 17 vertical lines.

The y-coordinates take values from 5 to 13.
We can draw lines parallel to x-axis corresponding to each of these values.
So, we will be able to draw 9 horizontal lines.

#### Key Question: What maketh a rectangle?

2 horizontal lines and two vertical lines will form a rectangle
Number of ways of selecting 2 horizontal lines from 9 horizontal lines = 9C2
9C2 = $$frac{9 × 8}{2}$ = 36 Number of ways of selecting 2 veritcal lines from 17 vertical lines = 17C2 9C2 = $\frac{17 × 16}{2}$ = 136 #### Number of rectangles that can be formed Product of the number of ways of selecting 2 horizontal lines and number of ways of selecting two vertical lines = 36 × 136 = 4896 #### Choice C is the correct answer. #### GMAT Online CourseTry it free! Register in 2 easy steps and Start learning in 5 minutes! #### Already have an Account? #### GMAT Live Online Classes Next Batch July 20, 2024 Work @ Wizako ##### How to reach Wizako? Mobile:$91) 95000 48484
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