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CBSE GMO 2015 Paper discussion

Group Mathematical Olympiad is conducted by CBSE . It is only for CBSE students . Every CBSE school can send 5 students for it. Around 30 students are selected from the country and are eligible to write INMO.

Note by Aditya Chauhan
1 year ago

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Answer to question 3. \[\frac{6l-1}{4l-3}=\frac{7k-5}{5k-3}\] After cross multiplication we get \[8k+l+lk=6\] Adding 8 to both sides \[8k+8+l+lk=14\] \[8(k+1)+l(1+k)=14\] \[(8+l)(1+k)=14\] Since \(l,k\) are integers therefore the solutions of \[(l,k)=(-1,1),(-6,6),(6,0),(-7,13),(-15,-3),(-22,-2),(-10,-8),(-9,-15)\] Therefore the required fractions are \[ 1,\frac{43}{31},\frac{5}{3},\frac{37}{27},\frac{13}{9},\frac{19}{13},\frac{61}{43},\frac{55}{39}\] Shivam Jadhav · 1 year ago

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@Shivam Jadhav Can anybody please post a proper solution for question \(4\) with explanation? Saurabh Mallik · 11 months, 1 week ago

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@Saurabh Mallik Number of ways of selecting points from points is 28C3=3276

Now, we will eliminate some conditions..

Number of ways of selecting all 3 as adjacent points is 28.

Number of ways of selecting 2 adjacent points and one not adjacent with them is 28×24=672

Number of ways of selecting two points opposite diametrically along with the third point not adjacent to the former points is 14×22=308.

Hence, the desired result will be 3276-28-672-308=2268 Manisha Garg · 11 months, 1 week ago

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Answer to question number 2. \[P_{1}(m)-P_{2}(n)=a_{1}-a_{2}=\frac{2(b_{2}-b_{1})}{m-n}\] This implies that \(a_{1}-a_{2}=even\). \[P_{1}(m)-P_{2}(n)=a_{1}+a_{2}=-2(m+n)\] This implies that \(a_{1}+a_{2}=even\). Hence proved. Shivam Jadhav · 1 year ago

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@Shivam Jadhav Shivam dud you gave GMO or RMO? Aakash Khandelwal · 1 year ago

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@Aakash Khandelwal RMO Shivam Jadhav · 1 year ago

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@Shivam Jadhav How many did you solve? Svatejas Shivakumar · 1 year ago

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@Svatejas Shivakumar 5 Shivam Jadhav · 1 year ago

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when will the results of gmo will be declared Nikhil Shah · 11 months, 2 weeks ago

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Is the answer to question 4 2268? Divyansh Choudhary · 1 year ago

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@Divyansh Choudhary Yes it is Adarsh Kumar · 11 months, 4 weeks ago

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@Adarsh Kumar Can you tell me what is the expected cutoff for gmo? Divyansh Choudhary · 11 months, 3 weeks ago

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I was able to do 4.5 questions do i stand a chance to get selected... Divyansh Choudhary · 1 year ago

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Can anyone tell the answer of 5th question Devansh Shah · 1 year ago

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@Devansh Shah it is 4/3 Aryan Goyat · 11 months, 2 weeks ago

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@Aryan Goyat I m getting 1/3 Devansh Shah · 11 months, 2 weeks ago

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@Devansh Shah see i can't post my solution because it is too long but you can verify it by construction. Aryan Goyat · 11 months, 2 weeks ago

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Answer to question 6. Let \[a=m+\frac{b}{c}\] where \(m\) is any integer and \[0<b<c\] . Then \[a(a-3{a})=( m+\frac{b}{c})( m-2\frac{b}{c}) \] \[m^{2}-\frac{bm}{c}+\frac{2b^{2}}{c^{2}}\]. \[m^{2}-\frac{2b^{2}-bcm}{c^{2}}\] Now, \(m\) is an integer . Let's consider \[ \frac{2b^{2}-bcm}{c^{2}}=k\] where \(k\) is an integer . After solving we get \[\frac{b}{c}=\frac{m+_{-}\sqrt{m^{2}+8k}}{4}\].....(I) But \[\frac{b}{c}<1\]....(II) Now putting value of \(\frac{b}{c}\) from (I) to (II). We get \[m+k<2\] Therefore there are infinitely many integers \(m,k\) such that \[m+k<2\]. Hence proved. Shivam Jadhav · 1 year ago

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@Shivam Jadhav @Shivam Jadhav This ques is a little different from the RMO one , we have to find all values of 'a' between 3 & 4. @Devansh Shah is right , there will be 4 values. Aditya Chauhan · 1 year ago

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@Shivam Jadhav Bro ur equation which is quadratic in m is wrong also we will get 4 values of a Devansh Shah · 1 year ago

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@Devansh Shah A general solution \[a=(2n+1)+0.5\] where \(n\) is a integer. Shivam Jadhav · 1 year ago

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@Shivam Jadhav you can try the 6 question posted by me they all are of gmo. Aryan Goyat · 11 months, 2 weeks ago

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@Shivam Jadhav m cant be 'any' integer as 3<a<4. So a will be 3.something or a = 3 + b/c Yatharth Chowdhury · 1 year ago

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