SOLUTION STEPS:
  - Write the digits in a place-value chart: ones . tenths hundredths thousandths.
  - 1 one -> 1 in the ones place. 2 tenths -> 2 in tenths. 5 hundredths -> 5 in hundredths. 1 thousandth -> 1 in thousandths.
  - The decimal is 1.251.