Help figuring out casting ratio.

I'm going to be casting something in smooth-on flexfoam-it IV. It has an 80a to 100b mixing ratio. So 5:4. I need to have a total of 700g of pourible material. I'm sure it's something obvious but I can't figure out how many grams of each I need to pour. If I just try to top off the difference like doing the 80% of 350g first then I will end up with having to do 120% of the other part to reach 700g again. This doesn't seem right... than you for any help.

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    Answer ✓
    take your ratio numbers, 4:5 or 5: 4, doesn't matter. make a fraction out of them by finding the denominator that will help find the whole. 4+5 = 9.
    4/9 + 5/9 = 9/9 or 1. The 700 grams would be your 1. so, 4/9 x 700=311.111111111 and 5/9 x 700= 388.888888889 add the two together and you get 700 grams. Easy breezy!!

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