KS2 Maths homework, ratio, Help!

[Blu]

DS was off for over a week and may have missed the method for this:

Mrs Choy spent exactly £10 on 100 eggs for her shop
Large eggs cost her 50p each
Medium eggs cost her 10p each
small eggs cost her 5p each

For two of the sizes she bought the same number of eggs.
How many of each size did she buy?

I did it, just guessed, really, by starting with the number of large eggs that would cost half the budget, then the same number of medium eggs, and made up rthe difference in price with small eggs, and it was right.

But what is the theory and method, and how do I explain to DS how to do this?

I think, in KS2, that the estimate, work it out, and then fiddle with the figures if they are not right is the way that will have been taught.

Is about having a feel for numbers, and working out what could be right

OK - that is the way that I did it!

Not by turning it into a simultaneous equation...

There will be several different correct answers and "think about it, have a stab at an answer and fiddle about with it" is the method they are going for.

If I'd been doing it, I would have said (something to the effect of) "we want the same number of large eggs and medium eggs. One large egg and one small egg together cost 60p. You can buy 16 large eggs and 16 medium eggs for £10 (16 * 60p = £9.60) leaving 40p over to spend on 8 small eggs (40p / 5p = 8)."

But "I am very lazy. One is a number, so let's say she bought one large egg and one medium egg, totalling 60p, then spent the remaining £9.40 on 188 small eggs." is perfectly valid too, as are other methods.

sorry, I meant your method was what was expected! Certainly wouldn't be doing simultaneous equations in KS2

Are there lots of answers? That all add up to exactly 100 eggs in total and £10?
I only got
10 large eggs
10 medium eggs and
80 small eggs

Oh, d'oh! I only half read. No, there should only be one right answer . They teach an official approach to solving these in KS3 but in KS2 just fiddling around is plenty.

Thank you!

There is a second result, I think.

There isn't enough information to solve using simultaneous equations, so I've created three different sets of solutions -
same number of large and medium,
same number of large and small,
same number of medium and small.

If the number of large and small is 0, then 100 medium eggs also cost £10.

Depending on how old KS2 kids are, the above is another way to tackle it, but I'm guessing my solution may be above the age of the child!

ooh, that's clever -
0 eggs in large and small and 100 medium!
V good!

2x large = £1
2x small = 10p
89x medium = £8.90
total = £10

1805 - but thats not 100 eggs.

Blu meant to say, same number of medium and small eggs ends up with nasty numbers, and I can't find a solution that doesn't involve parts of eggs, so think there are just the 2 possible answers, yours and mine.