A store owner buys cell phones for $40 and marks up the price by 25%. What is the sale price of a phone?

$50

Step-by-step explanation:

Price of the cell phone bought p = $40

% of markup in price = 25%

Selling price of the cell phone = p + (%)p

Selling price of the cell phone = P + (0.25)p

Selling price of the cell phone = p + 0.25p

Selling price of the cell phone = 1.25p

Selling price of the cell phone = 1.25 * $40

Selling price of the cell phone = $50

the solution of the equation is 2.23 ⇒ answer b

step-by-step explanation:

* lets revise the meaning of exponential function

- the form of the exponential function is y = ab^x, where a ≠ 0, b > 0 ,  

  b ≠ 1, and x is any real number

- it has a constant base b

- it has a variable exponent x

- to solve an exponential equation, take the log or ln of both sides,  

  and solve for the variable

* lets solve the problem

∵

- the base is 7 and the exponent is x

- insert ㏑ in both sides

∴

- use the rule

∴ x ㏑(7) = ㏑(77)

- to find x divide both sides by ㏑(7)

∴

* the solution of the equation is 2.23 to the nearest 2 decimal places