Question

Tính A:

A= 2.2 + 4.4. + 6.6 + ...................... + 60.60

Answer 1

\(A=4\left(1.1+2.2+....30.30\right)\) 

\(A=4\left(1.2+....+30.31-1-2-....-30\right)\Rightarrow\frac{A}{4}=1.2+...+30.31-\frac{30.31}{2}\) 

\(\frac{3}{4}A=1.2.3+2.3\left(4-1\right)+.....+30.31.\left(32-29\right)-\frac{30.31.3}{2}=30.31.32-\frac{30.31.3}{2}\) 

........

Answer 2

2.2 x 11 + 3.3 x 11 + 4.4 x 11 + 5.5 x 11 + 6.6 x 11

= 24.2 + 36.3 + 48.4 + 60.5 + 72.6 

= 60.5 + 48.4 + 60.5 + 72.6

= 221