Answer: See explanation
Step-by-step explanation:
a) A large pizza with one topping costs $15.50. A large pizza with 4 toppings costs $20.
A large pizza with one topping costs $15.50.
Using the formula for direct variation,
y = kx
where,
y = Cost of pizza
x = number of toppings
k = constant of proportionality
15.50 = 1k
k = 15.50
A large pizza with 4 toppings costs $20.
Using y = kx
20 = 4k
k = 20/4
k = 5
Here, the price does not vary directly with the number of toppings because the constant of proportionality is different.
b) A marathoner ran 5 miles in 40 minutes and 15 miles in 120 minutes.
Using y = kx
where,
y = 40
x = 5
y = kx
40 = 5k
k = 40/5
k = 8
Using y = kx
where,
y = 120
x = 15
y = kx
120 = 15k
k = 120/15
k = 8
The number of minutes vary directly with the number of miles. This is because the constant of proportionality is thesame in both cases.
Therefore, the second one(B) represents a direct variation and the first one (A) doesn't.
