At the hairdresser ,jenny had 27 centimeters cut off her hair. how many decimeters of hair did jenny have cut off

1 centimeter = 0.1 decimeter. So 27 centimeters = 2.7 decimeters

An easy way to figure out what conversion you are doing is with..
King Henry Doesn't Usually Drink Chocolate Milk.
KHDUDCM
The UDC stands for Unit, deci, and then centi. You always have the larger number on the left hand side of the scale and the larger number gets to be 1.
27 centimeters×(1 deci/ 10 centi)= 2.7 decimenters