• # question_answer The combined cost of 5 doors and 7 bells was Rs 2350 while the cost of 10 doors and 4 bells is Rs 2200. How much is the cost of 2 doors? A)  Rs 100              B)  Rs 240 C)  Rs 80               D)  Rs 120

$5D+7B=2350$                 ...(i) and           $10D+4B=2200$                ...(ii) On multiplying Eq. (i) by 2 and then subtracting Eq. (ii) from it, we get                                        $10D+14B=4700$ $\Rightarrow$   $-10D-4B=-2200$ $\Rightarrow$   $10\,B=2500$ $\therefore$      $B=250$ Now, from Eq. (i), we get $D=\frac{2350-7\times 250}{5}=\text{Rs}\,120$ $\therefore$      $2\,D=\,\text{Rs}\,\,240$