Word problem

A box contains 13 currency notes, which are either ₦50 or ₦20 notes.
The total value of the currency notes is ₦530. How many ₦50 notes are
in the box?

SOLUTION

Let the number of ₦50 notes be x and the number of ₦20 notes be y.

Number of notes = x + y = 13................(1).
Total value of the notes = 50x + 20y = 530................(2).
Multiply (1) by 20.
20x + 20y = 260................(3).
Subtract equation (3) from (2).
30x = 270.
X = 9.
Therefore,
9 + y = 13 ................(1).
Y= 13 - 9 = 4.
Hence, there are 9 ₦50 notes (and 4 ₦20 notes) in the box.

................................................
CHECK: 9 + 4 = 13, and (50 x 9) + (20 x 4) = 450 + 80 = 530.