5dm-20cm

To simplify the expression \( 5 \, \text{dm} - 20 \, \text{cm} \), we first need to convert the measurements to the same unit.

1. Convert decimeters (dm) to centimeters (cm): \[ 1 \, \text{dm} = 10 \, \text{cm} \] Therefore: \[ 5 \, \text{dm} = 5 \times 10 \, \text{cm} = 50 \, \text{cm} \]

2. Now subtract \( 20 \, \text{cm} \): \[ 50 \, \text{cm} - 20 \, \text{cm} = 30 \, \text{cm} \]

Thus, \( 5 \, \text{dm} - 20 \, \text{cm} = 30 \, \text{cm} \).