Question

Assume the Ziders continue to grow in the same pattern. How old would a Zider be that had 73 hairs?

Answer 1

Number of hairs in day 1 , a = 5.

Every day number of hairs increases by , d = 4.

So, it is an Arithmetic Progression with first term a = 5 and common difference d = 4.

So, number of hair in nth days is given by :

$a_n=a+(n-1)d\\\\a_n=5+(n-1)4$

Let, after x days number of hairs are 73.

$73=5+(x-1)4\\\\x-1=\dfrac{73-5}{4}\\\\x=18\ days$

Therefore, Zider is 18 days old.

Hence, this is the required solution.