ISEE Upper Level Quantitative : Equilateral Triangles

Study concepts, example questions & explanations for ISEE Upper Level Quantitative

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Example Questions

Example Question #27 :Geometry

is an equilateral triangle. Pointsare the midpoints of, respectively.is constructed.

Which is the greater quantity?

(a) The perimeter of

(b) Twice the perimeter of

Possible Answers:

(b) is greater.

(a) and (b) are equal.

(a) is greater.

It is impossible to tell from the information given.

Correct answer:

(a) and (b) are equal.

Explanation:

If segments are constructed in which the endpoints form the midpoints of the sides of a triangle, then each of the sides of the smaller triangle is half as long as the side of the larger triangle that it does not touch. Therefore:

The perimeter ofis:

,

which is twice the perimeter of.

Note that the fact that the triangle is equilateral is irrelevant.

Example Question #1 :Equilateral Triangles

Column AColumn B

The perimeter The perimeter

of a square with of an equilateral

sides of 4 cm. triangle with a side

of 9 cm.

Possible Answers:

There is not enough info to determine a relationship between the columns.

The quantity in Column B is greater.

The quantity in Column A is greater.

The quantities in both columns are equal.

Correct answer:

The quantity in Column B is greater.

Explanation:

Perimeter involves adding up all of the sides of the shape. Therefore, the square's perimeter isor 16. An equialteral shape means that all of the sides are equal. Therefore, the perimeter of the triangle isor 27. Therefore, Column B is greater.

Example Question #31 :Triangles

is an equilateral triangle. Pointsare the midpoints of, respectively.is constructed.

Which is the greater quantity?

(a) The area of

(b) Twice the area of

Possible Answers:

(a) is greater.

It is impossible to tell from the information given.

(a) and (b) are equal.

(b) is greater.

Correct answer:

(a) is greater.

Explanation:

If segments are constructed in which the endpoints form the midpoints of the sides of a triangle, then four triangles, congruent to each other and similar to the larger triangle, are formed. Therefore, one of these triangles - specifically,- would have one-fourth the area of. This meanshas more than twice the area of.

Note that the fact that the triangle is equilateral is irrelevant.

Example Question #1 :How To Find The Length Of The Side Of An Equilateral Triangle

Which of the following could be the three sidelengths of an equilateral triangle?

Possible Answers:

Correct answer:

Explanation:

By definition, an equilateral triangle has three sides of equal length. We can identify the equilateral triangle by converting the given sidelengths to the same units and comparing them.

我们可以消除下ing by showing that at least two sidelengths differ.

2 yards =feet.

Two sides have lengths 6 feet and 7 feet, so we can eliminate this choice.

4 feet =inches

Two sides have lengths 48 inches and 50 inches, so we can eliminate this choice.

5feet =inches

Two sides have lengths 48 inches and 60 inches, so we can eliminate this choice.

yards =feet

Two sides have lengths 4 feet and 5 feet, so we can eliminate this choice.

yards =feet =inches

All three sides have the same length, making this the triangle equilateral. This choice is correct.

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