How to automatically calculate from half of the default attribute price?

[oshi-nila]

I have set up Prestashop 1.6.1.4 with vegetables being my main product.My product attributes for each product are 1kg(default attribute),500grams,750grams,250grams and 100grams where I have set as product  combinations with impact on unit price.In  front end when I click the radio button for each attribute the price changes.Currently the price is set manually for each attribute combination for one product.

 

So my question is when I set the price for 1kg lets say for example Rs.200,and then when I click the 500grams attribute how to automatically have the price for 500grams as the half of the 1kg price?

 

Is this possible in back end and if not what are the ways that this could be achieved?

 

Thanks in advance for your help

[oshi-nila]

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