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Maybe my English was bad.

I took away 10 50-cent coins and replaced with 10 20-cent coins, and just couldn’t get the answer, until…

I took away 10 50-cent coins of value $5, and replaced with equal value of 20-cent coins, ($5 ÷ $0.20) = 25 coins

  20-cent 50-cent
Quantity at first 3u 4u
Quantity change +25 -10
Quantity in the end 7p = 3u + 25 5p = 4u – 10
  Multiply by 5 Multiply by 7
  35p = 15u + 125 35p = 28u – 70

28u – 70 = 15u + 125

13u = 195

1u = 15

Value of 20-cent coins at first -> 3u × $0.20 = $9

Value of 50-cent coins at first -> 4u × $0.50 = $30

Sum of money in the box -> $9 + $30 = $39

1 Reply 0 Likes ✔Accepted Answer

Thank you. It’s  like solving simultaneous equations. 

1 Reply 0 Likes

You are absolutely right.

With 2 unknowns and 2 equations, it is indeed solving simultaneous equations.

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Thanks alot for the answer. Appreciate it!

1 Reply 0 Likes

You are most welcome!

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