Cannot compute a formula to combine 50% Sample and 20% Sample to make it 100%

Hi guys,

I've encountered another problem. I don't even know if this is possible but anyway, I'll try my best to explain the situation.

Mix Proportion (%) 100% = 50% + 20% + 30%

Sieve Size Final Mix Product Sample A Sample B Sample C
37.5mm 100% passing 100% 100% 100%
19mm 94.7% passing 92% 100% 91%
9.5mm 74.9% passing 62% 100% 83%

Liquid Limit: 20.6 22 18 0
Plasticity Index: 3.0 3 3 0
Linear Shrinkage: 3.7 5 1.2 0

On my spreadsheet, I've got 50% of Sample A + 20% Sample B + 30% Sample C to make up a final mix product of 100%.

The Liquid Limit, Plasticity Index and Linear Shrinkage on the Final Mix Product is calculated by:

e.g. Linear Shrinkage of Final Mix Product = Linear Shrinkage of Sample A multiplied by 50% of Sample A and then divide the result by 100 PLUS Linear Shrinkage of Sample B multiplied by 20% of Sample B.

*Note the values on the above example are just random values I entered so they don't necessarily add up correctly.

The Excel allows the user to add up to 5 Samples to make up the final mix product. As you can see for Sample C, the values are zero. I want to ignore this during the calculation. Is there a way where Excel can ignore the 30% Sample C and only use the 50% and 20% Sample and make those two Samples equivalent to 100% and calculate the Liquid Limit etc.

Thanks so much guys. Your help will be much appreciated.