Yvaries jointly as x and z. y equals 70 when x equals 7 and z equals 2. find y when x equals 6 and z equals 4. y= ?

Hello from MrBillDoesMath!

 y = 120

Discussion:

"y varies jointly as x and  z"  ==>    y = k*x*z   where k is a constant

Substitute y = 70, x = 7, z = 2 in this equation to determine the value of k

y     = k *x * z

70   = k * 7 * 2   or

70 = 14k or

k = 5.

So  y = 5 *x * z is the equation of variation.

Substituting x = 6 and z =4 in the equation gives

y = 5 * x * z = 5 * 6 * 4 = 120

Thank you,

MrB

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional