1.

A pen costs Rs 11 and a notebook costs Rs 13. Find the number of ways in which a person can spend exactly Rs 1000 to buy pens and notebooks.

Answer»

Let pens be x and notebooks be y.

∴ 11x + 13y = 1000

11x = 1000 – 13y

when y = 5 then x = 85

Now every common number will occur at the interval of 11 × 13 = 143 is RHS starting with y = 5, RHS is

935, 792, ..., 66

∴ We obtain total 7 such ordered pairs.



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