If the expenditure of gas on burning 6 burners for 6 hours a day for 8 days is Rs. 450, then how many burners can be used for 10 days at 5 hours a day for Rs. 625 ?

Shortest method of doing this question is ,
$${\text{Put in }}\frac{{{{\text{M}}_1} \times {{\text{T}}_1} \times {{\text{D}}_1}}}{{{{\text{W}}_1}}}$$     = $$\frac{{{{\text{M}}_2} \times {{\text{T}}_2} \times {{\text{D}}_2}}}{{{{\text{W}}_2}}}$$
$$\eqalign{ & {\text{Formula}} \cr & {\text{So, }} \cr & {\text{Let number of burners}} \to {\text{B}} \cr & \frac{{{\text{6B}} \times {6_{{\text{hours}}}} \times {8_{{\text{days}}}}}}{{450}} = \frac{{{\text{B}} \times 10 \times 5}}{{625}} \cr & {\text{After solving }} \to {\text{B}} = 8 \cr} $$