Probability question

i wrote a story where 70 children are at camp for three weeks. i want only one girl to have a birthday during that time, but my editor thinks that's unlikely and wants me to change it. can anyone me with some percentages or probability in my favor? so much!

Step-by-step explanation:

Three weeks is 21 days.  There are 365 days in a year.  So the probability that a person's birthday is in those three weeks is 21/365.

The probability that exactly 1 person out of 70 has a birthday in that time can be found with binomial probability:

P = nCr pʳ (1−p)ⁿ⁻ʳ

P = ₇₀C₁ (21/365)¹ (1 − 21/365)⁷⁰⁻¹

P = 70 (21/365) (344/365)⁶⁹

P ≈ 0.0675

There is a 6.75% probability that exactly one of the 70 children has a birthday during those three weeks.

it will cost dollar $540

the living room is 3 which means if we divide 325/3 then we get $108

therefore if 1part of the living room cost $108 and 3 costed $325

then total 5part of the room will cost 5*108 which gives $540