Bir kırtasiyeci aldığı kalemlerin tanesini 2 liradan satarsa 40 lira kâr, 1,5 liradan
satarsa 20 lira zarar ediyor.
Bu kırtasiyeci kaç kalem alıp satmış-
tır?
A) 125 B) 120 C) 115 D) 110​

Option B: 120.

Step-by-step explanation:

I will answer in English

This problem can be translated to:

A man bought N pens, (at a cost C) if he sells each pen at 2 lira, he will have a profit of 40 lira.

If he sells each pen at 1.5 lira, he will loss a total of 20 lira.

We want to find N, the number of pens that he bought.

if he sells the N pens at 2 lira each, the revenue is:

N*2 lira

And the profit is the difference between the revenue and the cost, then the profit (40 lira in this case) is:

N*2 lira - C = 40 lira.

When he sells each pen at 1.5 lira the equation is:

N*(1.5 lira) - C = -20 lira.

Then we have two equations:

N*2 lira - C = 40 lira.

N*(1.5 lira) - C = -20 lira.

To solve this we need to isolate the variable C in one of the equations, i will isolate C in the second equation:

N*(1.5 lira) + 20 lira = C.

Now we can replace this in the first equation to get:

N*(2 lira) - (N*(1.5 lira) + 20 lira) = 40 lira.

We can solve this for N.

N*(2 lira) - N*(1.5 lira) - 20 lira = 40 lira

N*(2 lira - 1.5 lira) = 60 lira

N*(0.5 lira) = 60 lira

N = (60lira/0.5lira) = 120

N = 120

This means that he bought 120 pens.

The correct option is B.

is this part of a question or something