Question 490790
Investment: $20,000 Annual Income: $1,280
x = T-Bills, 5% yeild y = T-Bonds, 7% yeild z = Corp Bonds, 9% yeild
amount invested in t-bills must be 2 times the amount invested in Corp Bills.
Find the amount in each investment. 
I have two of the three equations:
x+y+z= 20,000
5x+7y+9z=128,000 
What would the third equation be?
y = 2*z
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Cheers,
Stan H.