**PROBLEM 7. a.** Recall that the Astronomical Unit (Earth-Sun distance) discussed in Problem 5 is 1.496 X 10^8 km, to four significant figures. Find the Earth-Sun distance in miles to three significant figures.

**Solution:**

1 AU = 1.496 X 10^8 km

= (1.496 X 10^8/1) X ( 1 mile/ 1.61 km)

= 9.29 X 10^7 miles (almost 93 million miles)

**b.**The chart that follows gives the mean distance in kilometers of each planet in the solar system from the Sun. Express these distances in AU, using a suitable number of significant digits.

**Solution: ** Since each distance in the table has three significant digits, and the factor unit
1 AU/ 1.49598 X 10^8 km has an exact number in the numerator and six significant digits in the denominator, the distances in AU can be given to three significant digits. Multiplying by the factor unit shown gives the following distances in AU: