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Plane geometry (polygons, triangles, angles) — ISEE Upper practice questions

Plane geometry (polygons, triangles, angles) on ISEE Upper Quantitative Reasoning covers rectangles, squares, triangles, and other polygons, including sides, perimeters, areas, and angle relationships. A student has to reason about how a change in length or width affects area, compare a rectangle with a square that shares a perimeter, and apply triangle facts without heavy calculation. Items appear as word problems or quantitative comparisons asking which quantity is larger. Common traps include mixing perimeter with area, treating a percent change in one side as the same change in area, and assuming equal perimeters mean equal areas. Answer choices are four labeled options, often with a cannot-be-determined choice on comparisons.

  • Section: Quantitative Reasoning 37 questions on the paper
  • 179 practice questions in the app

Sample questions

Question 1

A rectangle's length is decreased by 20%20\%, and its width is increased by 50%50\%. The area of the new rectangle is what percent of the area of the original rectangle?

  1. A70%70\%
  2. B100%100\%
  3. C120%120\%
  4. D130%130\%
Show answer

Answer: C — 120%120\%

The new length is 0.8 of the original and the new width is 1.5 of the original. The area scale factor is 0.8×1.5=1.20.8\times1.5=1.2, so the new area is 120%120\% of the original.

Question 2

A rectangle has length twice its width. A square has the same perimeter as the rectangle.

Column AColumn B
The area of the rectangleThe area of the square
  1. AThe quantity in Column A is greater
  2. BThe quantity in Column B is greater
  3. CThe two quantities are equal
  4. DThe relationship cannot be determined from the information given
Show answer

Answer: B — The quantity in Column B is greater

Let the rectangle's width be ww, so its length is 2w2w and its perimeter is 6w6w. The square's side length is 6w4=3w2\dfrac{6w}{4}=\dfrac{3w}{2}. The rectangle's area is 2w22w^2, while the square's area is 9w24\dfrac{9w^2}{4}, so Quantity B is greater.

Question 3

In triangle ABCABC, mA=50m\angle A=50^\circ and mB>mCm\angle B>m\angle C.

Column AColumn B
mBm\angle B6565^\circ
  1. AThe quantity in Column A is greater
  2. BThe quantity in Column B is greater
  3. CThe two quantities are equal
  4. DThe relationship cannot be determined from the information given
Show answer

Answer: A — The quantity in Column A is greater

Angles BB and CC sum to 18050=130180^\circ-50^\circ=130^\circ. If they were equal, each would be 6565^\circ. Since mB>mCm\angle B>m\angle C, angle BB must be greater than 6565^\circ, so Quantity A is greater.

Practice 179 Plane geometry (polygons, triangles, angles) questions in the app

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