For these statements, round each number to 2 significant figures, then write it out in full.

AIt will cost 3.18 billion to renovate the State's classrooms.
BThe area of Ghana is 23.9 million hectares.
CThe estimated population of Lagos in 2006 was about 16.06 million.
DOne barrel of oil has a volume of $1.5899 \times 10^{-1} m^3$.
EThe light from the Moon is $2.15 \times 10^{-6}$ times the light from the Sun.

f. The Sun is about $1.496 \times 10^8 km$ from the Earth.

To round a number to two significant figures, we identify the first two non-zero digits of the number. We then look at the third significant figure to decide whether to round up or keep the current value. If the third digit is 5 or greater, we increase the second digit by one; if it is less than 5, we keep the second digit as is. Finally, we convert the result into full decimal notation.

AFor $3.18 \text{ billion}$:

The first two significant figures are 3 and 1. The third figure is 8. Since $8 \geq 5$, we round the 1 up to 2.
Rounding gives $3.2 \text{ billion}$.
Full decimal form: $3,200,000,000$.

BFor $23.9 \text{ million}$:

The first two significant figures are 2 and 3. The third figure is 9. Since $9 \geq 5$, we round the 3 up to 4.
Rounding gives $24 \text{ million}$.
Full decimal form: $24,000,000$.

CFor $16.06 \text{ million}$:

The first two significant figures are 1 and 6. The third figure is 0. Since $0 < 5$, we keep the 16 as is.
Rounding gives $16 \text{ million}$.
Full decimal form: $16,000,000$.

DFor $1.5899 \times 10^{-1}$:

The first two significant figures are 1 and 5. The third figure is 8. Since $8 \geq 5$, we round the 5 up to 6.
Rounding gives $1.6 \times 10^{-1}$.
Full decimal form: $0.16$.

EFor $2.15 \times 10^{-6}$:

The first two significant figures are 2 and 1. The third figure is 5. Following the standard rounding convention of rounding up at 5, we round the 1 up to 2.
Rounding gives $2.2 \times 10^{-6}$.
Full decimal form: $0.0000022$.

f) For $1.496 \times 10^8$:
The first two significant figures are 1 and 4. The third figure is 9. Since $9 \geq 5$, we round the 4 up to 5.
Rounding gives $1.5 \times 10^8$.
Full decimal form: $150,000,000$.

Examples

Rounding is a vital skill in scientific data reporting, finance, and engineering. For example, if a researcher states that a chemical reaction occurs in $0.00000215 \text{ seconds}$, reporting it as $0.0000022 \text{ seconds}$ provides a more manageable figure while maintaining sufficient precision for general communication. Understanding these rules ensures that reports are readable and consistent with standardized conventions.