Question

a varies directly as b and inversely as the square of c, and a=10 when b=8 and c=2. Find a when b=20 and c=5.

Answer 1

the equation for directly is x=ky
so for this it would be a=bk
and for inverse it is x=y/k
so it would be a=c/k
you plug it in from there

Answer 2

But the inverse formula is y=k/x ....

Answer 3

a = kb + k/c^2
10 = 8k + k / 4
40 = 32k + k
k = 40/33

a = (40/33)b + (40/33)/ c^2
when b=20 and c = 5

a = (40/33)*20 + (40/33) / 25
= 800/33 + 40 / (33*25)

Answer 4

- i get that to 24.29