I would say origin, but it's a hard choice.
Answer:
Question 1: 15 cups
20% (pineapple juice) = 3 cups, 100/20=5, 5*3 = 15 cups
Question 2: 20 cups
25% (orange juice) + 5% = 30%
30% (orange juice) = 6 cups, 30/6=5%, 100/5=20
I can't explain the whole thing very clearly, but hope it helped
Do u know the area of a circle
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Answer:

Variable is a symbol that represents a quantity in a mathematical expression, as used in many sciences. Variable (research), a logical set of attributes. Variable star, a type of astronomical star.

A constant, sometimes also called a "mathematical constant," is any well-defined real number which is significantly interesting in some way. A function, equation, etc., is said to "be constant" (or be a constant function) if it always assumes the same value independent of how its parameters are varied.