Question

y and x have a proportional relationship, and y = 15 when x = 3. What is the value of x when y = 4?



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y and x have a proportional relationship, and y = 12 when x = 5. What is the value of y when x = 8?



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Answer 1

Y and x have a proportional relationship, and y = 15 when x = 3. What is the value of x when y = 4?

y = kx
15 = 3k
k = 15/3
k = 5
so
What is the value of x when y = 4?
y = kx
4 = 5 * x
x = 4/5
x = 0.8

answer
x = 0.8 when y = 4
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y and x have a proportional relationship, and y = 12 when x = 5. What is the value of y when x = 8?

y = kx
12 = 5k
k = 12/5
k = 2.4

so
What is the value of y when x = 8?

y = kx
y = 2.4 * 8
y = 19.2

answer
y = 19.2  when x = 8

Answer 2

The value of x when y = 4 is 4/5

The value of y when x is 8 is 7.5

Direct and inverse variation

If y and x have a proportional relationship and y = 15 when x = 3, hence;

y =  kx

k = k/x

k = 15/3

k = 5

If y = 4, the value of x is calculated as:

x = y/k

x = 4/5

Hence the value of x is 4/5

Similarly, if y and x have a proportional relationship, and y = 12 when x = 5, hence;

y = k/x

k = yx

k = 12 * 5

k = 60

The value of y when x is 8 is expressed as:

y = 60/8

y = 7.5

Hence the value of y when x is 8 is 7.5

Learn more on variation here: https://brainly.com/question/1603692