Answer:
y=kx
subst y=10 and x=20 into the above
10=k20
k=10/20
k=1/2
therefore relationship: y=1/2x
subst x=15 into the relationship
y=1/2(15)
y=7,5
Step by step explanation:
- Step 1: when they say y varies directly with x they mean y is proportional to x
- step 2: so y=kx where k is the constant
- step 3: is to substitute y=10 and x=20 into the above equation y=kx
- step 4: you will end up with 10=k20 then divide both sides by 20 so that k becomes the subject of the formula
- step 5: your answer from the above will be k=10/20 so the relationship is y is directly proportional to 1/2 x what you did here is that you substituted k for 1/2 in the equation in step 3
- step 6: is to finally substitute x=15 into the equation y=1/2x to finally get your answer y=7,5.
