How does Russell determine the birthdays by examining the numbers? (info in description)

homework

1 Answer
Jul 23, 2018

Subtract #205# which will give us last two digits as day and first one or two digits as month.

Explanation:

Let the month be #m# and day be #d#.

First step gives us #5m+7#.

Second step gives us #(5m+7)xx4=20m+28#

Third step gives us #20m+28+13=20m+41#

Fourth step gives us #(20m+41)xx5=100m+205#

and fifth step gives us #100m+205+d#

So first subtract #205# which will give us #100m+d# and we get last two digits as day and first one or two digits gives us month.

In first case for Dave we get #612-205=407#, hence #7^(th)# April, in second case of Ricky, we get #1129-205=924#, hence #24^(th)# September and in the case of Mike, we get #1436-205=1231# i.e. #31^(st)# December.