A penny weighs 5.8×10−3

To find out how many pennies are in a pile that weighs \( 3.596 \times 10^4 \) lb, you can use the formula:

\[
\text{Number of pennies} = \frac{\text{Total weight of pennies}}{\text{Weight of one penny}} = \frac{3.596 \times 10^4 \text{ lb}}{5.8 \times 10^{-3} \text{ lb/penny}}
\]

Now calculate the division step by step:

1. First, find the division of the coefficients:

\[
\frac{3.596}{5.8} \approx 0.620
\]

2. Then, perform the division of the powers of ten:

\[
\frac{10^4}{10^{-3}} = 10^{4 - (-3)} = 10^{4 + 3} = 10^7
\]

3. Combine the two results:

\[
\text{Number of pennies} \approx 0.620 \times 10^7
\]

To express this in proper scientific notation, we rewrite \( 0.620 \) as \( 6.2 \times 10^{-1} \):

\[
0.620 \times 10^7 = 6.2 \times 10^{-1} \times 10^7 = 6.2 \times 10^{7 - 1} = 6.2 \times 10^6
\]

Therefore, the number of pennies in the pile is:

\[
\boxed{6.2 \times 10^6}
\]