SOLUTION: Find two positive numbers satisfying the given requirements. The sum of the first and twice the second is 120 and the product is a maximum.

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Question 1125335: Find two positive numbers satisfying the given requirements.
The sum of the first and twice the second is 120 and the product is a maximum.

Found 2 solutions by greenestamps, MathLover1:
Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


Let the numbers be x and y. Then we know

x%2B2y=120
2y+=+120-x
y+=+60-x%2F2

So the second number is 60-x/2.

We want the product of the two numbers to be a maximum. The product is

x%2860-x%2F2%29+=+-%281%2F2%29x%5E2%2B60x

The maximum/minimum value of the quadratic expression ax^2+bx+c is when x = -b/2a. In this problem, that is

-60%2F-1+=+60

So the first number is 60 and the second is 60-30 = 30. The product is 1800.

Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!

let first number be x, and second number y
given:
x%2B2y=120...solve for y
2y=120-x
y=60-x%2F2...eq.1

the product is a maximum:
P=xy...substitute y from eq.1
P=x%2860-x%2F2%29
P=+60x-x%5E2%2F2
P=+-%281%2F2%29x%5E2%2B60x...............find first derivative (if you are familiar with it)
P'= -2%281%2F2%29x%2B60
P'= -x%2B60
max is at P'=0
0=+-x%2B60
x=60
go to x%2B2y=120, find y
60%2B2y=120
2y=120-60
2y=60
y=30

your numbers are: 60 and 30