Robbie bought the smallest amount. Let's use x for that amount.
Let's use n for amount that each following customer increases.
We have:
Robbie=x
Cameron=x+n
Louis=x+n+n
Tom=x+n+n+n
Charlie=x+n+n+n+n
We know that they bought total of 60 scones.
Robbie + Cameron + Louis + Tom + Charlie = 60
x + x+n + x+n+n + x+n+n+n + x+n+n+n+n = 60
5x + 10n = 60 /:5
x + 2n = 12
We are also given this information:
(Robbie + Cameron) = 3/7 * (Louis + Tom + Charlie)
We insert the equations from above:
(x + x+n) = 3/7 * (x+n+n + x+n+n+n + x+n+n+n+n)
2x + n = 3/7 * (3x + 9n) /*7
14x + 7n = 3* (3x + 9n)
14x +7n = 9x + 27n
We take everything on the left side.
14x + 7n - 9x - 27n = 0
5x - 20n = 0/:5
x - 4n = 0
Now we have two equations:
x + 2n = 12
x - 4n = 0
We solve second one for x and insert it into first one.
x + 2n = 12
x = 4n
4n + 2n =12
6n = 12 /:6
n = 2
x=4*2
x=8
Now we can solve for the amount for each customer.
Robbie=x = 8
Cameron=x+n = 8 + 2 = 10
Louis=x+n+n = 8 + 2 + 2 = 12
Tom=x+n+n+n = 8 + 2 + 2 + 2 = 14
Charlie=x+n+n+n+n = 8 + 2 + 2 + 2 + 2 = 16
There are 3 parts to the ratio so...
First we divide the total number of objects we are sharing (in this case 15 biscuits) by the number of parts in the ratio (3)
15 / 3 = 5
Then we know that each part of the ratio is worth 5 biscuits. So we times each part of the ratio by how many biscuits are in one part...
1 x 5 = 5
2 x 5 = 10
So when the biscuits are shared into the ratio 1:2, the number of biscuits in each are 5:10
Hope this helps :)
