Question

X is directly proportional to y. When x = 4, y = 7. Work out the value
of y when x = 12

Answer 1

y = 21

Explanation:

When x is directly proportional to y:

When x increases, y also increases.

In this case, it is so you write,

1. Write down the formula: y=kx

k being the constant.

Let's use "When x = 4, y = 7" to work out the constant.

2. Substitute the 'when' values: 7=k×4

3. Rearrange to find the constant: 7÷4=k

4. Find k: k=1.75

Now let's see the new problem, 'what is y when x = 12'.

5. Substitute the values now but keep the constant: y = 1.75 × 12

6. Rearrange if needed.

7. Find the missing value: y = 21

Hope this helped and if you require further assistance from me please comment below! :)

Ps: If it was inversely proportional then the formula would be y = k / x

with k still being the constant.