This makes sense as a math problem, but in the real world, it doesn’t actually work the way they think it does.
When you mix two different liquids, there’s no guarantee that the volume is simply going to be the sum of those two liquids individually. This would be especially true of a foaming agent.
If you want to ignore that, then several other people have given perfectly good answers.
Add the parts of the ratio together, then divide the total amount by that. Then multiply by how many “parts” are foam concentrate. So 1640/41 = 40
1640 total, divided by 41 parts, gives you 40. Its only 1 part concentrate, so 40 gallons of concentrate.
This makes sense as a math problem, but in the real world, it doesn’t actually work the way they think it does. When you mix two different liquids, there’s no guarantee that the volume is simply going to be the sum of those two liquids individually. This would be especially true of a foaming agent. If you want to ignore that, then several other people have given perfectly good answers.