<PRE><B>Question 880944</B>
4/10 are new

Is he replacing old ones with new ones or just adding new ones?
If he replaced old with new then he bought 4 new ones and threw out 4 old old ones leaving two old ones and 8 new ones.

If he kept the old ones,
(4+x)/(10+x)=8/10
40+10x=80+8x
2x=40
x=20
So if he kept the old ones he bought 20 new ones
check
(4+20)/(10+20)=24/30=8/10
6 of the 30 are still old





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