Sunday Times Teaser 2523
by Danny Roth
Published: 30 January 2011 (link)
George and Martha moved to a two-figure house number in Unusual Avenue. The avenue runs from south to north and each house is directly opposite another. No 1 is the southernmost on the west side, then the houses run consecutively up the west side, then southwards back down the east side. So, No 1 is opposite the highest-numbered house. George and Martha’s number is a multiple of the number of the house opposite. The same is true of the five houses their daughters live in, but all their houses have three-figure numbers.
How many houses are there in the avenue?