Let's solve each part of the question in detail:

a) Write $1.54 \times 10^4$ as an ordinary number.

To convert from scientific notation to an ordinary number, move the decimal point to the right by the power of 10:

• $1.54 \times 10^4 = 15400$.

b) Write $5.09 \times 10^{-3}$ as an ordinary number.

For a negative exponent, move the decimal point to the left by the power of 10:

• $5.09 \times 10^{-3} = 0.00509$.

c) Write 540000 in standard form.

To express in scientific notation, place the decimal after the first non-zero digit and count the places:

• $540000 = 5.4 \times 10^5$.

d) Write 0.000869 in standard form.

Move the decimal after the first non-zero digit:

• $0.000869 = 8.69 \times 10^{-4}$.

Summary of Answers:

• a) $15400$
• b) $0.00509$
• c) $5.4 \times 10^5$
• d) $8.69 \times 10^{-4}$

Would you like more details or have any questions?

Here are some related questions to practice:

1. Convert $3.7 \times 10^6$ to an ordinary number.
2. Write $0.00034$ in standard form.
3. Convert $8.5 \times 10^{-2}$ to an ordinary number.
4. Write 67000000 in standard form.
5. Express $4.56 \times 10^{-4}$ as an ordinary number.

Tip: When converting from scientific notation, remember that a positive exponent moves the decimal to the right, while a negative exponent moves it to the left.