calculate

[enthada]

A certain type of mixture is prepared by mixing brand A at $.9 a kg. with brand B at $.4 a kg. If the mixture is worth $.7 a kg., how many kgs. of
brand A are needed to make 40kgs. of the mixture?

[Fibonacci]

the mixture costs $7 so the mxture will have A & B in the ratio 3:2 (3/5 of 9 + 2/5 of 4 = 7)
40kgs / 5 = 8kg
8 x 3 = 24kg of A costs $216
8 x 2= 16Kg of B costs $64
40kg of mixture cost $280 (that's $7 per kg)

answer 24kgs of brand A