February 19, 2013

On George Washington’s 281st birthday, we posted the following math problem:

- 4 farthings = 1 penny
- 2 half pennies (pronounced hay-pennies) = 1 penny
- 12 pence (pennies) = 1 shilling
- 10 shillings and 6 pence = ½ guinea
- 20 shillings = 1 pound
- 21 shillings = 1 guinea

George left his home in Mount Vernon one morning, and on the way to work decided to stop and buy a few gifts for his wife, Martha. He bought her a checkerboard that cost 2 shillings, 6 pence, 1 farthings and a fancy new dress that cost 1/2 guinea and 9 shillings. He gave the shopkeeper 1 pound and 1 guinea.

- How much was his purchase in pence?
- What is the smallest amount of change he could have received?

Here’s how we answered it:

The checkerboard cost 2 shillings, 6 pence, 1 farthing

2 shillings = 24 pence + 6.25 pence = 30.25 pence

The dress cost 1/2 guinea and 9 shillings

1/2 guinea = 10 shillings 6 pence = 126 pence

9 shillings = 108 pence

Cost of dress in pence: 234 pence

Total cost: 30.25 + 234 = 264.25 pence

The president gave the shopkeeper 1 pound and 1 guinea

1 pound = 20 shillings = 240 pence

1 guinea = 21 shillings = 256 pence

240 + 256 = 492 pence

His change would be:

492 – 264.25 = 227.75

That can be made with 1 half guinea, 2 shillings, 5 pence, 1 halfpenny, and 1 farthing.