Taking The Shopping Challenge

What was the problem?

Let N = number of notebooks, P = number of pens & E = number of erasers.

From the given maths we get 2 equations as,

N + P + E = 100................(1)

15N +1P +E/4=100…....(2)
 
From (1),

P = 100 - N - E

From (2),

60N + 4P + E= 400

60N + 4(100-N-E) + E = 400

60N + 400-4N-4E + E = 400

56N - 3E = 0

56N = 3E

N/E = 3/56

From the ratio, we get, N=3, E=56.

Putting these in equation (1),

We get,

P=41.

So we should buy 56 erasers,41 pens & 3 notebooks to satisfy the given condition.