If there are two numbers next to each other, use a combination of numerals and characters for clarification.
   There were twenty 6-foot-high posts used for the fence.
   They gave away 123 ten-page booklets.

If a sentence starts with a number and another number is separated by no more than three words, use text for both. Otherwise a number starting a sentence has no affect on the other number styles.
   Thirty men and forty women attended the event.
   Fifty years ago they saw an eclipse and the next one won’t occur for another 40 years.