Question

z varies inversely with the product of x and y. when x=2 and y=4, z=0.5. what is the value of z when x=4 and y=9? please help, i've tried different things and i can't seem to get the correct answer. my choices are a: 45/2 b: 40/9 c:40 d: 1/9

Answer 1

I will try thinking of it this way.
Z varies INVERSELY with the product of x and y.
This means, if x*y is more, then z will be less.
At hand, we have
x = 2 and y = 4
So, x*y = 2*4 = 8
And, z = 0.5

Now, when
x = 4 and y = 9
x*y = 4*9 = 36

Now since the product is greater in the second case (36>8), the value of z should be lower than 0.5

Let's look at the options.
a. 45/2 = 22.5 --> Not possible, it is greater than 0.5
b. 40/9 = 4.44 --> Again, greater than 0.5
c. 40 --> Much bigger than 0.5
d. 1/9 = 0.11 --> Could be possible, since it is lesser than 0.5

Now since the product is bigger in the second case, the value of z MUST be smaller than 0.5

So, I think the correct answer is D. 1/9

Hope this helps! :)

Answer 2

ohhhhh okay. i think i get it. thank you.