5. The speed of sound depends on the type of medium and the temperature of the medium it is traveling through. The speed of sound in dry air at 15°C is about 1 227·93 kilometres per hour. Rewrite this number in the form a × 10n where 1 ≤ a < 10, and n ∈ ℕ.
,
6. A human heart beats an average of 80 beats per minute. How many beats is this in an hour? Express your answer in the form a × 10n
, where 1 ≤ a < 10, and n ∈ ℕ.
7. The average person blinks 17 times per minute. How many times does the average person blink in a three-hour period when awake? Express your answer in scientifi c notation.
8. The number of molecules in 1 gram of water is 3·34 × 10 22
Express this number as a regular number.
19.2 Multiplying variables with powers
By the end of this section you should be able to: ● multiply variables with powers
Discuss and discover From 19.1, we know that indices (or exponents or powers) are numbers that tell us how often a number is to be multiplied by itself in a mathematical expression.
Working with a classmate, copy and complete the table below. Expanded form
p × p × p
5 × 5 Written as a power of 5 = Written as a power of p =
4 × 4 × 4 Written as a power of 4 = 6 × 6 × 6 × 6 Written as a power of 6 = y × y × y a3 a2 x3
× a
× a2 × x4
304 Linking Thinking 1
Written as a power of y = Written as a power of a = Written as a power of a = Written as a power of x =
Index form 5 2 p3
Look carefully at the table to see if you can discover a rule (using powers) to fi nd the missing answers.
What have you learned about multiplying terms and powers from completing this table?