Answer: Option B: 120.
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.