Question

The value of y varies directly with x. If x = 3, then y = 21. What is the value of x when y = 105?

Answer 1

Answer: 15

Step-by-step explanation:

varies directly means: $\frac{y}{x} = k$

Plug in the given values of x and y to solve for k: $\frac{21}{3} = k$  → 7 = k

Next, plug in the k-value of 7 and the given y value of 105 to solve for x:

$\frac{105}{x} = 7$

$\frac{105}{x}(\frac{x}{7}) = 7(\frac{x}{7})$

$\frac{105}{7} = x$

15 = x