Total
expenses of a boarding house are partly fixed and partly varying linearly with
the number of boarders. The average expense per boarder is Rs.
700 when there are 25 boarders and Rs.
600 when there are 50 boarders. What is the average expense per boarder when
there are 100 boarders?

(a).
550

(b)
580

(c)
540

(d).
570

Let
the
fixed income be x and the number of boarders be y.