Alan

xy=20     (1)

x+y=-19     (2)    

From (2) we have y = -x -19    (3)

Use (3) in (1)

x*(-x - 19) = 20

-x^2 - 19x = 20 

rearrange

x^2 + 19x + 20 = 0

Use the quadratic equation

x = (-19 +/- sqrt(19^2 - 4*1*20))/2

to obtain:

x₊ = (sqrt(281) - 19)/2

x_- = -(sqrt(281) + 19)/2

Put these back into (3) to get the corresponding values of y.

You need to supply more information!

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Depends on the function. What one did you have in mind?

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You've missed a minus sign in the original equation Guest#1

7x - 3x - 4 = -2x + 5x - 2

4x - 4 = 3x - 2

Subtract 3x from both sides and add 4 to both sides:

x = 2

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Calculate the index of refraction:  sin(25)/sin(16.7) ≈ 1.47

This is the index of refraction of Pyrex.

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Absolute = 44 - 25

Relative = 44/25 - 1

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Let b = number of 2 wheel bikes, t = 3 wheel trikes, f = 4 wheel bikes

b + t + f = 95

2b + 3t + 4f = 250

b = t + 20

You now have three independent equations in three unknowns.  Can you take it from here?

" (Some irrational numbers are 'repeating' but some are not,like pi for example.)"

Note that no irrational numbers are repeating.  If they were they would be expressible as the ratio of two integers; i.e. they would be rational!

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5 out of every 8 are hot, so the total number of hot drinks = 400*5/8 → 250

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Yes.    m₁*v₁ + m₂*v₂