A metallurgist has one alloy containing 23 % aluminum and another containing 69 % aluminum. How many pounds of each alloy must he use to make 54 pounds of a third alloy containing 55 % aluminum? (Round off the answers to the nearest hundredth.)

hello from mrbilldoesmath!

answer:

a(n) - a(n-1) -3

discussion:

this ones a bit interesting. given a(n) = 5 - 3n consider this:

a(n-1) = 5 - 3(n-1)

          = (5 - 3n) + 3             => but a(n) = 5 - 3n, the first term

          = a(n)   + 3                 => subtract 3 from both sides

a(n-1) -3 = a(n)  

or

a(n) - a(n-1) -3

you,

mrb

the answer is 37

step-by-step explanation: