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A certain square is to be drawn on a coordinate plane : GMAT Problem Solving (PS)

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A certain square is to be drawn on a coordinate plane [#permalink]
14 Sep 2010, 21:06

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A certain square is to be drawn on a coordinate plane. One of the vertices must be on the origin, and the square is to have an area of 100. If all coordinates of the vertices must be integers, how many different ways can this square be drawn?

I'll post the official explanation, but it doesn't make sense to me

Each side of the square must have a length of 10. If each side were to be 6, 7, 8, or most other numbers, there could only be four possible squares drawn, because each side, in order to have integer coordinates, would have to be drawn on the x- or y-axis. What makes a length of 10 different is that it could be the hypotenuse of a Pythagorean triple, meaning the vertices could have integer coordinates without lying on the x- or y-axis.

For example, a square could be drawn with the coordinates (0,0), (6,8), (-2, 14) and (-8, 6). (It is tedious and unnecessary to figure out all four coordinates for each square).

If we label the square abcd, with a at the origin and the letters representing points in a clockwise direction, we can get the number of possible squares by figuring out the number of unique ways ab can be drawn.

a has coordinates (0,0) and b could have the following coordinates, as shown in the picture:

Re: MGMAT How many squares? [#permalink]
14 Sep 2010, 21:16

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jpr200012 wrote:

A certain square is to be drawn on a coordinate plane. One of the vertices must be on the origin, and the square is to have an area of 100. If all coordinates of the vertices must be integers, how many different ways can this square be drawn?

(A) 4 (B) 6 (C) 8 (D) 10 (E) 12

This question becomes much easier if you visualize/draw it.

Let the origin be O and one of the vertices be A. Now, we are told that length of OA must be 10 (area to be 100). So if the coordinates of A is (x, y) then we would have x^2+y^2=100 (distance from the origin to the point A(x, y) can be found by the formula d^2=x^2+y^2)

Now, x^2+y^2=100 has several integer solutions for x and y, so several positions of vertex A, note that when vertex A has integer coordinates other vertices also have integer coordinates. For example imagine the case when square rests on X-axis to the right of Y-axis, then the vertices are: A(10,0), (10,10), (0,10) and (0,0).

Also you can notice that 100=6^2+8^2 and 100=0^2+10^2, so x can tale 7 values: -10, -8, -6, 0, 6, 8, 10. For x=-10 and x=10, y can take only 1 value 0, but for other values of x, y can take two values positive or negative. For example: when x=6 then y=8 or y=-8. This gives us 1+1+5*2=12 coordinates of point A:

x=10 and y=0, imagine this one to be the square which rests on X-axis and to get the other options rotate OA anticlockwise to get all possible cases; x=8 and y=6; x=6 and y=8; x=0 and y=10; x=-6 and y=8; x=-8 and y=6; x=-10 and y=0; x=-8 and y=-6; x=-6 and y=-8; x=0 and y=-10; x=6 and y=-8; x=8 and y=-6.

Re: MGMAT How many squares? [#permalink]
14 Sep 2010, 21:22

Bunuel wrote:

jpr200012 wrote:

A certain square is to be drawn on a coordinate plane. One of the vertices must be on the origin, and the square is to have an area of 100. If all coordinates of the vertices must be integers, how many different ways can this square be drawn?

(A) 4 (B) 6 (C) 8 (D) 10 (E) 12

This question becomes much easier if you visualize/draw it.

Let the origin be O and one of the vertices be A. Now, we are told that length of OA must be 10 (area to be 100). So if the coordinates of A is (x, y) then we would have x^2+y^2=100 (distance from the origin to the point A(x, y) can be found by the formula d^2=x^2+y^2)

Now, x^2+y^2=100 has several integer solutions for x and y, so several positions of vertex A, note that when vertex A has integer coordinates other vertices also have integer coordinates. For example imagine the case when square rests on X-axis to the right of Y-axis, then the vertices are: A(10,0), (10,10), (0,10) and (0,0).

Also you can notice that 100=6^2+8^2 and 100=0^2+10^2, so x can tale 7 values: -10, -8, -6, 0, 6, 8, 10. For x=-10 and x=10, y can take only 1 value 0, but for other values of x, y can take two values positive or negative. For example: when x=6 then y=8 or y=-8. This gives us 1+1+5*2=12 coordinates of point A:

x=10 and y=0, imagine this one to be the square which rests on X-axis and to get the other options rotate OA anticlockwise to get all possible cases; x=8 and y=6; x=6 and y=8; x=0 and y=10; x=-6 and y=8; x=-8 and y=6; x=-10 and y=0; x=-8 and y=-6; x=-6 and y=-8; x=0 and y=-10; x=6 and y=-8; x=8 and y=-6.

Answer: E.

hey Bunuel Thanx,but can u please come out with a Image,only 2 or 3 coordinate value drawn in it....i am sooooo confused....

Re: MGMAT How many squares? [#permalink]
15 Sep 2010, 08:42

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Expert's post

thirst4edu wrote:

Bunuel wrote:

sandeep800 wrote:

hey Bunuel Thanx,but can u please come out with a Image,only 2 or 3 coordinate value drawn in it....i am sooooo confused....

All 12 squares.

Image posted on our forum by GMATGuruNY:

Attachment:

square.PNG

Question says "One of the vertices must be on the origin", then why center of square is at origin of co-ordinate system? Shouldn't one of the vertices (the corner) of the square be at the origin?

Each diagram shows 4 squares not 1, so if you take first diagram you'll see 4 squares and each has one vertex at the origin. _________________

Re: MGMAT How many squares? [#permalink]
14 Oct 2010, 14:19

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Best way is to find for one quadrant and multiply by 4.

6,8 satisfy the point for the vertex of the square.

=> 8,6 will also satisfy => 2 squares per quadrant ---> if you are confused why this is true then draw the x-y axis and try to visualize what happens when x is replaced with y. => 4*2 = 8 squares

Now 10,0 also satisfy the point or the vertex. but when we will replace x with y the same square is generated => 10,0 and 0,10 are part of same squares. => 1 per quadrant => 4*1 = 4 squares

Re: MGMAT How many squares? [#permalink]
14 Oct 2010, 14:27

I got this question on a MGMAT CAT as well, but I refuse to believe a question this hard can be on the real GMAT. It is not obvious at all how to solve this in a straight forward manner. _________________

Re: MGMAT How many squares? [#permalink]
14 Oct 2010, 15:13

shrouded1 wrote:

I got this question on a MGMAT CAT as well, but I refuse to believe a question this hard can be on the real GMAT. It is not obvious at all how to solve this in a straight forward manner.

I got this on my first Mgmat Cat as well. Most of the questions are time consuming in Mgmat cat's. Have you seen similar level of mgmat cat in Gmat? _________________

Re: coordinate geometry [#permalink]
22 Dec 2010, 13:27

Expert's post

Merging similar topics.

TheBirla wrote:

Great approach nookway, but in the 2nd part of your your solution, you are assuming the 4rth vertex is also an integer. And though your assumption is correct, i.e. the 4rth vertex is (14,2) , (2,14) and so on and so forth, I am not sure if this is a 2 minute problem and i got this in one of the mock CAT's that i was doing. Is this the level of problems one has to expect if you are aiming for a 750 + ? Thanks.

As for your question I doubt that this is a realistic GMAT question. Though if you find that # of squares should be multiple of 4 you'll be left with A, C and E choices right away. Next, you can also rule out A as at least 2 squares per quadrant can be easily found and then make an educated guess for E thus "solving" in less than 2 minutes. Refer for complete solution to the posts above. _________________

Re: coordinate geometry [#permalink]
22 Dec 2010, 13:40

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TheBirla wrote:

Great approach nookway, but in the 2nd part of your your solution, you are assuming the 4rth vertex is also an integer. And though your assumption is correct, i.e. the 4rth vertex is (14,2) , (2,14) and so on and so forth, I am not sure if this is a 2 minute problem and i got this in one of the mock CAT's that i was doing. Is this the level of problems one has to expect if you are aiming for a 750 + ? Thanks.

So you don't need to find the 4th vertex and hence don't need to spend that time. You just need to figure out the integral values of x and y such that x^2 + y^2 = 100 which is quite straight forward. Take x = 0. y = 10 satisfies. Now check for x = 1/2/3 etc which will take just a few secs each. You will see that x = 6 and y = 8 satisfies.

x can be 0/10/6/8, y will be 10/0/8/6 or -10/-8/-6. Taking negative sign of x, you will get: x = -10/-6/-8 and y will be 0/8/6 or -8/-6.

Total 12 such squares.

And yes, it is one of the tougher questions, definitely above 700. _________________

Re: MGMAT How many squares? [#permalink]
22 Dec 2010, 15:03

Thanks a lot Bunuel and Karishma.

Karishma, took me a while to get my head around the solution (symmetry of squares), but once i did its just given me a different perspective for these sort of problems. Great approach ! And thanks once again.

A certain square is to be drawn on a coordinate plane. One [#permalink]
01 Nov 2012, 07:14

A certain square is to be drawn on a coordinate plane. One of the vertices must be on the origin, and the square is to have an area of 100. If all coordinates of the vertices must be integers, how many different ways can this square be drawn?

a)4 b)6 c)8 d)10 e)12 _________________

Bole So Nehal.. Sat Siri Akal.. Waheguru ji help me to get 700+ score !

Re: A certain square is to be drawn on a coordinate plane. One [#permalink]
01 Nov 2012, 07:17

Expert's post

sanjoo wrote:

A certain square is to be drawn on a coordinate plane. One of the vertices must be on the origin, and the square is to have an area of 100. If all coordinates of the vertices must be integers, how many different ways can this square be drawn?

a)4 b)6 c)8 d)10 e)12

Merging similar topics. Please ask if anything remains unclear. _________________

Re: A certain square is to be drawn on a coordinate plane [#permalink]
25 Jan 2013, 06:32

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jpr200012 wrote:

A certain square is to be drawn on a coordinate plane. One of the vertices must be on the origin, and the square is to have an area of 100. If all coordinates of the vertices must be integers, how many different ways can this square be drawn?

(A) 4 (B) 6 (C) 8 (D) 10 (E) 12

To construct a square, we think of one of its side which is a line from (0,0) to some (x,y). Since the area of the square is 100, its side will have a side = 10. We can use the distance formula: d^2 = x^2 + y^2 Thus, 100 = x^2 + y^2

Let's think of combinations of perfectly squared x and y that adds up to 100. {0,10} and {6,8} The best way to think of these combinations is to list the perfect squares and experiment on the combinations that adds up to 100.

Now {0,10}, Both numbers could be x,y or reversed and 10 can be negative or positive. Thus, we already have 2*2 = 4 points. Now {6,8}, Both numbers could be x,y or reversed and 6 and 8 could be negative or positive. Thus, we have 2*2*2 = 8points

And your possible points that form a distance of 10 from the (0,0)... 4+8 = 12

A certain square is to be drawn on a coordinate plane. One [#permalink]
27 Mar 2013, 21:40

A certain square is to be drawn on a coordinate plane. One of the vertices must be on the origin, and the square is to have an area of 100. If all coordinates of the vertices must be integers, how many different ways can this square be drawn? (A)4 (B)6 (C)8 (D)10 (E)12 Need help

gmatclubot

A certain square is to be drawn on a coordinate plane. One
[#permalink]
27 Mar 2013, 21:40

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