230

300

320

400

3(1)+3(2)+3(3)+3(4)+3(5)

3(1)+3(2)+3(3)+3(4)

5(1)+5(2)+5(3)

5(1)+5(2)+5(3)+5(4)+5(5)

(10-2(1)) + (10-2(2)) 

(10-2(1)) + (10-2(2)) + (10-2(3))

(10-3(1)) + (10-3(2)) + (10-3(3))

(10-3(1)) + (10-3(2)) 

40

50

60

70

$\sum_{i=1}^ni\ =\ \frac{n}{2}\left(n+1\right)$

$\sum_{i=1}^ni\ =\ \frac{n}{2}\left(n+2\right)$

$\sum_{i=1}^ni^2\ =\ \frac{\left(n\right)\left(n+1\right)\left(2n+1\right)}{2}$

$\sum_{i=1}^ni^2\ =\frac{\left(n\right)\left(n+1\right)\left(n+2\right)}{6}$

$\sum_{i=1}^ni^2\ =\frac{\left(n\right)\left(n+1\right)\left(2n+1\right)}{6}$

$\sum_{i=1}^{10}4i\ =\ 4\sum_{i=1}^{10}i\$

$\sum_{i=8}^{12}\frac{i}{3}\ =\ \frac{1}{3}\sum_{i=8}^{12}i\ \ \$

$\sum_{i=3}^4i\left(i+1\right)=\left(\sum_{i=3}^4i\right)\left(\sum_{i=3}^4i+1\right)$

$\sum_{k=1}^5k\left(k^2-7\right)\ =\ \left(\sum_{k=1}^5k\right)\left(\sum_{k=1}^5k^2-7\right)$

$\sum_{k=3}^4k\left(k+1\right)\ =\sum_{k=3}^4k^2+k\$

Kahoot!

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