IELTS Grammar: be careful with the 's'

 Notice where we put the "s" on the end of a word and where we don't:

• Thousands of people watched the show.
• Fifty thousand people watched the show.
• over a period of ten years
• over a ten-year period
• The fish weighed 5 kilos.
• It was a five-kilo fish.
• The boy is three years old.
• He is a three-year-old boy.