Hi this might be simple but unsure how to do it.

I need to enter a product which is priced like this

1 x Product £5.50

2 x Products £10.00

So adding two of the same product to the cart deducts 50p

How would I set this up without using attributes? Or if using attributes then how would I ensure that selecting 2 products from attributes functions in the same way as adding 2 products in the quantity box?

Thanks

nick