📚 How to combine approximate and exact numbers when considering significant digits

An approximate number is a measured number that always has some uncertainty in the rightmost digit. That is, we cannot be sure of its exact value. On the other hand, an exact number is one that has no uncertainty.

Some examples of exact numbers are:

○ There are exactly 24 hours in a day, no more, no less.
○ Most automobiles have exactly four wheels.

When you are combining an exact number and an approximate one, the accuracy of the result will be limited by the approximate number, so you treat the exact number has having more significant figures than any of the approximate numbers in that computation.

Q1. If a certain car tire weighs 32.2 lb., how much will four such tires weigh?

Q2. One inch equals exactly 2.54 cm. Convert 385.84 in. to centimeters.

Q3. Express 2 hr. and 35.8 min in minutes.

We must add an exact number (120 minutes) and an approximate number 35.8 minutes). Since 120 is exact, we retain as many decimal places as in the approximate number, 35.8.

Q4. Multiplying the exact number 3 by the approximate number 6.836.

[carolinariba]

Thank you so much!! I was searching for operations of significant figures that included exact numbers but couldn't find anywhere. Your video really helped