If a · b = 20, a = 4, and the angle between the vectors a and b is 30°, what is the magnitude of vector b? Incorrect: Your answer is incorrect.

The magnitude of is approximately 5.774.

Explanation:

According to the definition of dot product:

Where:

, - Norms (or magnitudes) of and , dimensionless.

- Internal angle between and , measured in sexagesimal degrees.

The magnitude of is therefore cleared:

Given that , and , the magnitude of is:

The magnitude of is approximately 5.774.

0.11 m/s and 0.28 m/s should be correct

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form