Question

The average (arithmetic mean) of y numbers is x. If 30 is added to the set of numbers, then the average will be x − 5. What is the value of y in terms of x ?

Answer 1

Answer:

y = $\frac{1}{5}(x^{2}-35x)$

Step-by-step explanation:

Let the total numbers are n.

If the average of y numbers is x then we can form an equation

$\frac{y}{n}=x$

⇒ $\frac{n}{y}=\frac{1}{x}$

⇒ n = $\frac{y}{x}$ --------(1)

Now 30 is added to the set of numbers then average becomes (x - 5)

$\frac{y+30}{n+1}=(x-5)$

⇒ $\frac{(n+1)}{(y+30)}=\frac{1}{(x-5)}$

⇒ (n + 1) = $\frac{y+30}{x-5}$

⇒ n = $\frac{y+30}{x-5}$ - 1 ----- (2)

Now we equate the values of n from equation 1 and 2

$\frac{y}{x}$ = $\frac{y+30}{x-5}$ - 1

y(x - 5) = x(y + 30) - x(x - 5)  [ By cross multiplication ]

xy - 5y = xy + 30x - x² + 5x

xy - xy - 5y = 35x - x²

-5y = 35x - x²

x² - 35x = 5y

y = $\frac{1}{5}(x^{2}-35x)$

Answer 2

Answer: y = x/5 - 7

Step-by-step explanation:

Please see the workings attached .