A right triangle has sides of a, b, and 11, respectively,

A pythagorean triplet involving 11 is (11,60,61) . Since, the other two sides are integers, hence this satisfies. and we have 60+61=121 in the option (Although,I do not advocate the usage of this fundamental in solving the questions , but if one is through with basic pythagorean triplets then it would really help in saving some valuable time)

It is debatable if a three sided figure with one zero length is a triangle. Is this question GMAT worthy?

The length must be greater than 0. The sides are {11, 60, 61}: each sides is greater than 0. Don't see any problem with this question.

is there any shor trick to solve this type of question?

Veritas Prep Official Solution:

Since the first two right triangles with integer sides are the 3-4-5, the 6-8-10, and the 5-12-13, 11 cannot be the hypotenuse. Hence 11 is one of the legs, and our equation is \(11^2 + a^2 = b^2.\) Subtracting a^2 from both sides gives us \(11^2 = b^2 - a^2\), or \(121 = (b + a)(b - a)\). Since b and a are both positive integers, (b + a) must = 121 and (b - a) must = 1. (The only other option, (b+a)=(b-a)=11 is impossible with positive a.) Hence \((b + a) = 121\).

I did not understand the Veritas official explanation for this, they have taken the standard ratios - 3-4-5, 5-12-13 and determine on the basis of those, that the hyp cannot be 11, could someone explain this reasoning?

The trick for this question is

If the side of a right angle triangle is a prime number then other two sides will be

Second Side = [(Prime)^2 + 1]/2

Third Side = [(Prime)^2 - 1]/2

i.e. for One side = 11

Second Side = (11^2 -1)/2 = (121-1)/2 = 60
Third Side = (11^2 +1)/2 = (121+1)/2 = 61

I hope this helps!

I personally find it an UNSUITABLE question for GMAT... GMAT Doesn't expect such tricks from students.

First, if all you know is that the length of one side is prime, there are infinitely many possible lengths for the other sides. It's only if you know the other sides are integers that there might be a formula.

But you also mean to say "if the shortest side of a right triangle is prime, and the other sides are of integer length, the other sides will be..." If all you know is that one side is of length 5, say, using your formulas you'd think the other sides need to be 12 and 13. They could also be 3 and 4.



No one will ever need the formulas you posted in a GMAT question, and it would be pointless for a test taker to memorize them. But you certainly don't need those formulas here. You only need to know the difference of squares factorization, and that there is only one way to write 11^2 as a product of two distinct positive integers. The question is well within the scope of the GMAT.

You seem of have less understanding of the word "OPINION"

I hope you prove me wrong by bringing ONE question from authentic source of GMAT questions if you have enough exposure of GMAT.(Refer OG, GMAT PREP etc.)

Another point, whether you take (3, 4, 5) or (5, 12, 13) it fit in both cases. and the forward application doesn't approve of backward application as well. (1 is a natural no. doesn't mean that a natural no. has to be 1)

And yes, It fit's to the cases when the smallest side is prime Number and the all Sides are of Integer length so I must admit you are good at finding faults and not as good in appreciating a new concept and an opinion.

I'm afraid I don't understand your reply. In your first post, you said that when "the side of a right angle triangle is a prime number then other two sides will be" x and y. That is, you said we can determine the other two sides from one side, when the length of that one side is prime. That's not true, but if a test taker believed it was, he or she might answer questions incorrectly on the GMAT - for example, a DS question like the following:

If the lengths of the three sides of a right triangle are integers, what is the perimeter of the triangle?
1. The length of one side is 5
2. Two of the lengths are prime numbers

A test taker who thinks that a single prime length is sufficient to determine the other two will think Statement 1 is sufficient, and will pick A, which is not the right answer - the answer is E, since the triangle might be a 3-4-5 or 5-12-13 triangle. I will always post a clarification if an expert here posts something which might be misinterpreted, and which might lead a test taker to answer test questions incorrectly, and I'd always be grateful to anyone who posts a clarification of one of my posts if I were ever to make an error.

I also don't understand why you think I confused your statement with its converse (what you're suggesting in your comment about natural numbers). I did not. Nor do I understand why you consider it relevant that the 3-4-5 triangle fits your formula, since we don't find the lengths 3 and 4 by plugging in '5', but regardless there are other triangles with a prime length that do not satisfy those formulas - the 8-15-17 triangle, for example.



I don't think it often is a matter of opinion whether a question falls within the scope of the GMAT. It's not clear to me precisely why you think this question is out of the scope of the test. I agree with you when you say, referring to your formulas, that "GMAT Doesn't expect such tricks from students." That seemed to me the only reason you described this question as "unsuitable" for the test. But those formulas aren't at all necessary here, so I disagreed with your initial premise. The main mathematical issue in this question, when solving it using the difference of squares factorization, is recognizing that when b > c > 0, and b and c are positive integers, the equation (b+c)(b-c) = 121 has only one possible solution. If you want to see an official question that relies on very similar logic, see this one from GMATFocus:

if-x-and-y-are-integers-such-that-x-y-0-what-is-x-156464.html

IanStewart: Thumbs up! I agree with your perspective too.

A right triangle has sides of a, b, and 11, respectively, where a and b are both integers. What is the value of (a + b)?

A) 15
B) 57
C) 93
D) 109
E) 121

Hi, could you then please elaborate a bit more on the solution proposed above? How can we reach the conclusion that 11 is not the hipotenuse?

Thanks you are definitely a star. My knowledge of pythagorean triplet is a bit rusty, I didn't consider that if there is not a triplet (or a multiple) with 11 in the hypotenuse then 11 can't be the hypotenuse of a right triangle given the constraint that all the sides need to be integers

Thanks again

Its answer E

1. Check with recycled triangles 3:4:5/6:8:10/5:12:13 --> 11 cannot be the hypotenuse
2. 11 is one of the legs, so the equation is 11²+a²=b² ==> b²-a²=11²
3. Reminds me of recycled quadratic III (a+b)(a-b)=a²-b² and apply to above (works in 99% of cases)
4. (b+a)(b-a)=11²=121 / factorize 121 in factor tree leaves me only with 121 1, so (b+a) must be 121 since a and b are defined as integeres

Time: 50 sec

So if a and b both are integers, then a+b should also be integer. Now we are asked to find the value of (a+b)^2. I started POE. None of the values is a perfect square (which one square root result into a integer, which should be the value of base a+b) EXCEPT 121.

I am pretty sure it cant be that simple, what am i missing here

How do you figure that we are looking for (a + b)^2?
We are looking for the value of (a + b) only.