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Ram divided $15$ pennies among four small bags.
He labelled each bag with the number of pennies inside it.
He could then pay any sum of money from $1$p to $15$p without opening any bag.
How many pennies did Ram put in each bag?
This problem is based on Money Bags from 'Mathematical Challenges for Able Pupils Key Stages 1 and 2', published by DfES. You can download a copy here.