Brain-Teaser 460

From The Sunday Times, 22nd March 1970 [link]

Boppo is made up in 1 lb cans at 8s, 2 lb cans at 15s and 4 lb cans at 27s. The contents of crates vary, but every crate contains 60 cans of mixed three sizes with a total value of £45.

The foreman himself had packed two such crates. He told new worker Rob, “Just go along and nail down those two open crates in the shed, Rob. The lorry’s waiting.”

Rob found the two crates standing beside the weighing platform, and for no particular reason he weighed them. One was heavier than the other. “Huh! Calls ‘isself a foreman” he said, as he removed some cans from the heavier crate. “That’s it. Both the same now. Lucky I weighed ’em”. So he nailed them down and the lorry went off with them.

He met the foreman. “You made a mistake with those crates, chum”, he said, “but it’s OK now. Here’s three spare cans.”

“!!” said the foreman.

What were the weights of the two crates the foreman had packed?