Height of a palm Tree

       A Palm tree was 90 cm high, when it was planted.

          It grows by an equal number of cms each year, and at the end of the seventh year it was one ninth taller than at the end of the sixth year. Can you tell how tall the tree was at the end of the twelfth year?

Answer:  450 Centimetres. Supposing the tree grows x centimetres each year. Height of the tree at the end of sixth year = (90 + 6x) cm

Growth in the seventh year x = 1/9 (90 + 6x) cm

X = 10 + 2/3 x

X = 30

The height of the tree at the end of the twelfth year = (90 +12 x 30) cm = 450 cm