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# Simultaneous equations watch

1. anybody help with this one Its been a long long time since I was at school
I think its a 3 variable Simultaneous equation but that's as far as I can get

Sophie, Rita and Dave are counting the change they each have. When they add it all together it comes to exactly £10.00. They each decide to put a portion of there own money into a charity box.
Sophie decides to put in 10% of her money,
Rita decides she will put in 50% of hers,
Dave decides on 90% of his.
Sophie and Rita each calculate the total amount that the friends have given but cannot agree on the sum.
It transpires that Sophie’s answer is correct and Rita has calculated 10% of her change and 40% of Sophies change.
Both of them have correctly calculated 50% of Dave’s change.
What is the smallest and largest amount of change that Dave could have been carrying?
2. What have you done so far?
3. Start by writing that out in terms of equations.
4. Could you clarify - you say "Dave decides on 90% of his change", but then "they both correctly calculate 50% of Dave's change". Which of these values is correct? Or have I misunderstood something?
5. *their
6. (Original post by spocckka)
*their

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