(10 + 15 + 20 + ... + 95 + 100) x = 1045

Đáp án:

x=1

Giải thích các bước giải: $\begin{array}{l}10{\rm{ ; }}15{\rm{ ; }}20;{\rm{ }}...{\rm{ ; }}95;100\,\,\,\,la\,\,\,day\,\,cach\,\,deu\,5\,don\,vi\\SSH = \left( {so\,c{\rm{oo}}i\, - \,so\,dau} \right):khoang\,cach\, + 1\\\,\,\,\,\,\,\,\,\,\,\, = \,\,\left( {100 - 10} \right):5 + 1 = 19\,\,\,\left( {so\,\,hang} \right)\\ \Rightarrow 10{\rm{ }} + {\rm{ }}15{\rm{ }} + {\rm{ }}20{\rm{ }} + {\rm{ }}...{\rm{ }} + {\rm{ }}95{\rm{ }} + {\rm{ }}100 = \frac{{10 + 100}}{2} \times 19 = 1045\\ \Rightarrow \left( {10{\rm{ }} + {\rm{ }}15{\rm{ }} + {\rm{ }}20{\rm{ }} + {\rm{ }}...{\rm{ }} + {\rm{ }}95{\rm{ }} + {\rm{ }}100} \right){\rm{ }}x{\rm{ }} = {\rm{ }}1045\\ \Leftrightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,1045x\,\,\,\,\,\,\,\,\,\,\,\, = \,\,\,\,\,\,1045\\ \Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x = 1\end{array}$