Answer:
Ian collected 171 stamps
Explanation:
let the number of stamps Jed collected be n , then
Janet collected 3n ( three times as many as Jed ) and
Ian collected 3n - 21 ( 21 less than Janet )
sum the three collections and equate to total collected 427
n + 3n + 3n - 21 = 427
7n - 21 = 427 ( add 21 to both sides )
7n = 448 ( divide both sides by 7 )
n = 64
Then
Ian collected 3n - 21 = 3(64) - 21 = 192 - 21 = 171