Red is 17 years younger than Sepia. If Sepia's age is written after Red's, the result is a 4-digit perfect square. The same situation recurs after 13 years. Find the age of Red if Sepia is older than 30.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Let the ages of Red and Sepia be r and s respectively, Then s = r + 1 7 and that
{ 1 0 0 r + s = 1 0 1 r + 1 7 = m 2 1 0 0 ( r + 1 3 ) + s + 1 3 = 1 0 1 r + 1 3 3 0 = n 2 . . . ( 1 ) . . . ( 2 ) where n > m are positive integers.
( 2 ) − ( 1 ) : n 2 − m 2 ( n − m ) ( n + m ) = 1 3 1 3 = 1 3 × 1 0 1 Note that 13 and 101 are primes.
Assuming { n − m = 1 3 n + m = 1 0 1 ⟹ m = 4 4 ⟹ m 2 = 1 9 3 6 ⟹ r = 1 9 .