78 is a very important number because it is the sum of the last two digits in the year. It also happens to be the sum of the first four digits in the decade. For example, 1978 is a 78 because it is the sum of 1978 (the last two digits) and 1987 (the first four digits). In addition, 78 is also the sum of the first two digits in each month and day.

### What are the factors of 78?

The factors of 78 are 1, 2, 3, 5, 8, 13, and 21.

### What is the area of a circle with radius 5?

The area of a circle with radius 5 is 120.

### What is the area of a circle with radius 10?

The area of a circle with radius 10 is 100.

### What is the cost of a copy of the book?

The cost of a copy of the book is $10.

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