if i have 5 days to sell 200 tickets by friday how many tickets do i have to sell the first day if i sell ten less then the previous day

something is missing here.

like what

how many tickets do i have to sell the first day if i sell ten less then the previous day

that makes no sense. There is no previous day to the first day.

Monday you sold x tickets

Tuesday you sold x-10
wedn ... x-20
thu ... x-30
frid ...x-40

x + x-10 + x-20 + x-30 + x-40 = 200
5x - 100 = 200
x = 60

On the first day you had to sell 60 tickets.

check:
What is 60+50+40+30+20 ?

To find out how many tickets you need to sell on the first day, let's work backwards from Friday.

We know that you need to sell a total of 200 tickets by Friday. Let's break it down day by day:

Friday: You should reach your target of 200 tickets by the end of the day.
Thursday: The day before Friday, you would have sold a certain number of tickets. Let's call this number X.
Wednesday: The day before Thursday, you would have sold 10 less than the previous day, so X - 10 tickets.
Tuesday: The day before Wednesday, you would have sold 10 less than the previous day, so (X - 10) - 10 tickets.
Monday: The day before Tuesday, you would have sold 10 less than the previous day, so ((X - 10) - 10) - 10 tickets.

Now, since you need to sell a total of 200 tickets, the sum of the tickets sold on each day should add up to 200:

((X - 10) - 10) - 10 + (X - 10) - 10 + X = 200

Simplifying the equation, we have:

3X - 60 = 200

To isolate X, we add 60 to both sides of the equation:

3X = 260

Finally, dividing both sides by 3, we get:

X = 260 / 3 = 86.666...

Since you cannot sell a fraction of a ticket, we can round X down to the nearest whole number:

X = 86

Therefore, you need to sell 86 tickets on the first day in order to meet your target of 200 tickets by Friday.