Is That too Much to Calculate?(1)

Algebra Level 2

Observe the following: 1 = 1 2 1=1^2

2 + 3 + 4 = 3 2 2+3+4=3^2

3 + 4 + 5 + 6 + 7 = 5 2 3+4+5+6+7=5^2

4 + 5 + 6 + 7 + 8 + 9 + 10 = 7 2 4+5+6+7+8+9+10=7^2

\dots\dots 2018 + 2019 + 2020 + . . . . . . . . . . . . . . . . . . . . . + 6052 = n 2 2018+2019+2020+.....................+6052 = n^2 what is n = ? n=?


The answer is 4035.

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3 solutions

Matin Naseri
Aug 18, 2018

( 6052 + 6051 + + 2020 + 2019 + 2018 ) ( 2017 + 2016 + + 5 + 4 + 3 + 2 + 1 ) = n 2 (6052+6051+{\dots}+2020+2019+2018)-(2017+2016+{\dots}+5+4+3+2+1) = n^2

n ( n + 1 ) 2 \frac{n(n+1)}{2}

6052 ( 6052 + 1 ) 2 = 18316378 \frac{6052(6052+1)}{2}={\boxed{18316378}}

2017 ( 2017 + 1 ) 2 = 2035153 \frac{2017(2017+1)}{2}={\boxed{2035153}}

18316378 2035153 = 16281225 18316378 - 2035153={\boxed{16281225}}

16281225 = n 2 16281225=n^2

n = 16281225 = 4035 n = {\sqrt{16281225}} ={\boxed{4035}}

\color{#3D99F6}{\therefore} the answer is 4035 \color{#3D99F6}{\boxed{4035}}

Nice solution.(+1)

Tom Clancy - 2 years, 9 months ago
Daniel Sikora
Aug 20, 2018

I have just simply take the arithmetic average in the way from the taken numbers as shown: n 2 = ( 2018 + 6052 2 ) 2 = 4035 2 n^{2}=(\frac{2018+6052}{2})^{2}={\color{#D61F06}4035}^{2} , what is probably the less advanced way to solve it. The red number is our answer.

Ram Mohith
Aug 18, 2018

If you observe carefully the number of terms in every sequence is the square of the resulting number . 1 ( 1 t e r m ) = 1 2 1 \quad ({\color{teal}1}~term) = {\color{teal}1}^2

2 + 3 + 4 ( 3 t e r m s ) = 3 2 2 + 3 + 4 \quad ({\color{#E81990}3}~terms) = {\color{#E81990}3}^2

3 + 4 + 5 + 6 + 7 ( 5 t e r m s ) = 5 2 3 + 4 + 5 + 6 + 7 \quad ({\color{#3D99F6}5}~terms) = {\color{#3D99F6}5}^2

4 + 5 + 6 + 7 + 8 + 9 + 10 ( 7 t e r m s ) = 7 2 4 + 5 + 6 + 7 + 8 + 9 + 10 \quad ({\color{#D61F06}7}~terms) = {\color{#D61F06}7}^2

\dots \dots

2018 + 2019 + 2020 + . . . . . . . . . + 6052 ( n t e r m s ) = n 2 2018 + 2019 + 2020 + ......... + 6052 \quad ({\color{#20A900}n}~terms) = {\color{#20A900}n}^2 Now, we have to find the value of n n .


The numbers 2018 , 2019 , 2020 , . . . . . , 6052 2018, 2019, 2020 , ..... , 6052 are n \color{#20A900}n terms in arithmetic progression with a = 2018 , d = 1 a = 2018, d = 1 . The last term in an A.p is given by the formula :

T n = a + ( n 1 ) d T_n = a + (n - 1)d

6052 = 2018 + ( n 1 ) 1 n + 2017 = 6052 \implies 6052 = 2018 + ({\color{#20A900}n} - 1)1 \implies {\color{#20A900}n} + 2017 = 6052

n = 4035 \implies \boxed{\color{#20A900}n = 4035}

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