SOLUTION: A telephone box accepts only 20p coins or 50p coins. on one day 39 coins were collected with a total value of 11.40pounds. Find how many 50p coins were collected. This question is

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Question 235854: A telephone box accepts only 20p coins or 50p coins. on one day 39 coins were collected with a total value of 11.40pounds. Find how many 50p coins were collected.
This question is from the chapter "simultaneous equations"
This question is extremely difficult for me that I am incapable of solving it. Therefore I request you to solve it as soon as possible.

Answer by checkley77(12844) About Me  (Show Source):
You can put this solution on YOUR website!
x+Y=39 or x=39-y
.20x+.50y=11.40
.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