Question

7+14+21+......+2002=
calculati

Answer 1

$S=7+14+21+...+2002= \\ \\ ~~~=7(1+2+3+...+286)= \\ \\ ~~~=7 \cdot \frac{286 \cdot 287}{2}= \\ \\ ~~~= 7 \cdot 143 \cdot 287= \\ \\ ~~~=1001 \cdot 287= \\ \\ ~~~=287287.$

Answer 2

7(1+2+3+.....286)= 7*286*287/2=287287