# Problem of the Week ## Coal Statistics

In 2021, Australia consumed 1.63 exajoules of coal. This is the quantity of energy produced by the coal.

1 exajoule = 1 000 000 000 000 000 000 joules

1 gigajoule = 1 000 000 000 joules

How many gigajoules is equivalent to 1.63 exajoules?

Because we have a base 10 numeration system, every time a number is multiplied by 10, each digit in the number is worth 10 times more.

When a digit is worth 10 times more, it moves one place to the left.

Therefore, when a number is multiplied by 10, all its digits move one place to the left.

1 gigajoule multiplied by 10, 9 times gives 1 exajoule.

1 exajoule divided by 10, 9 times gives 1 gigajoule.

1 exajoule = 1 000 000 000 gigajoules

1.63 exajoules = 1.63 x 1 000 000 000 gigajoules

= 1 630 000 000 gigajoules

The number of times the digits are multiplied by 10, can also be expressed as a power of 10, so

1 exajoule = 1 x 1018 joules

1 gigajoule = 1 x 109 joules

1 gigajoule x 109 = 1 exajoule

i.e. 1 exajoule = 109 gigajoules

1.63 exajoules = 1.63 x 109 gigajoules