Question

if x varies directly as the sum of reciprocals of y and z, and x=7 when y=2 and z=5 find the value of y when x=20 and z=2

Answer 1

Answer:

x proportional to 1/y + 1/z

which gives 7 proportional to 1/2 + 1/5

7 proportional to 7/10

hence k=1/10

with the given condition, 20=(1/10) (1/y + 1/2)

That gives y=2/399

Answer 2

Answer:

y = 2/3

 

Step-by-step explanation:

x = k(1/y + 1/z)

 

7 = k(1/2 + 1/5)

 

7 = (7/10)k

So, k = 10

x = 10(1/y + 1/z)

 

If x = 20 and z = 2, we have 20 = 10(1/y + 1/2)

1/y + 1/2 = 2

1/y = 3/2

y = 2/3