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  Number & Math Play

The Wall
Q If the Jones twins can build a wall five bricks long and five bricks high in 1 minute, how long will it take them to build a wall ten bricks long and ten bricks high?

A The first wall has 25 bricks. The second wall has 100 bricks ? four times as many. So it will take four times as long ? that is, four minutes.

Source: David Adler,Easy Math Puzzles