a parking meter accepts only 20p coins or 50p coins. On one day, 39 coins were collected with a total value of $11.40. find how many 50p coins were collected.

x + Y = 39 or x = 39-y

20x + 50y = 1.40

20 (39 - y) + 50y = 11.40

7.80 - 20y + 50y = 11.40

30y = 11.40 - 7.80

30y = 3.60

y = 3.60/30

y = 12 50p coins were collected.

x = 39 - 12 = 27 20p coins were collected.

Proof:

20*27 + 50*12 = 11.40

5.40 + 6 = 11.40

11.40 = 11.40

I hope it helps.