Answer-
He must use 75 pound of first kind and 25 pound of second kind tea.
Solution-
Price of first kind tea per pound = $0.32
Price of second kind tea per pound = $0.40
By selling it at $0.43 per pound he made a profit of 25%
Let the cost price is x, then
[tex]\Rightarrow x+\dfrac{25}{100}x=0.43\\\\\Rightarrow \dfrac{125}{100}x=0.43\\\\\Rightarrow x=0.43\times \dfrac{100}{125}\\\\\Rightarrow x=34[/tex]
The cost price of the mixed kind is $0.34
Then, let the amount of first kind tea in the 100 pound mixture is y pound, so the amount of second kind tea is (100-y) pound
So, the price of mixture will be equal to the sum of price of each kind,
[tex]\Rightarrow 0.32y+0.40(100-y)=0.34\times 100[/tex]
[tex]\Rightarrow 0.32y+40-0.40y=34[/tex]
[tex]\Rightarrow 0.08y=6[/tex]
[tex]\Rightarrow y=\dfrac{6}{0.08}=75[/tex]
[tex]\Rightarrow y=75[/tex]
[tex]\Rightarrow (100-y)=100-75=25[/tex]
Therefore, he must use 75 pound of first kind and 25 pound of second kind tea.