To find the ratio between online sales to shop sales, we first need to find the number of shop sales. We can do this by subtracting the the number of online sales from the total number of sales. Substituting the values given by the problem, we get 240-180 which means that 60 necklaces were sold in the shop. To find the ratio of online sales to shop sales, we can just put a colon in between the two quantities. This gives us 180:60. But, this is not simplifies. Since both numbers are multiples of 60, we can divide each side by 60 to get our final answer of 3:1.