Question

If y varies directly as x and y-21 when x is 7, find x when y = -5.

Answer 1

Answer:

X=-5/3

Step-by-step explanation:

Y=KX where k is constant

y=kx

21=7k divide both sides by 7

to get 3

then equate

to get answer

Answer 2

Step-by-step explanation:

Since, y varies directly as x:

$\therefore \: y = kx..(1) \\ (k = constant \: of \: proportionality) \\ at \: y = 21 \: and \: x = 7 \\ 21 = k \times 7 \\ k = \frac{21}{7} = 3 \\ plugging \: k = 3 \: in \: equation \: (1) \\ y = 3x..(2) \\ plugging \: \: y = - 5 \: in \: (2)\\ - 5 = 3x \\ x = \frac{ - 5}{3} \\ \: \: \: \: \: \: \huge \red{ \boxed{x = - \frac{5}{3} }}$