# Rate problems 0.5

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Rate is one of the very useful concept in Math. The rate is defined as the ratio between two different quantities. The quantities such as miles, centimeters, minutes, seconds and so on. Ratio is the quantitative comparison between the given quantities. For the quantities the unit rate is calculated by the ratio of two different quantities are compared to a unit measure of one of the quantity. Some examples how the unit rates are expressed are centimeter per minute written as cm/min; kilometers per second written as km/sec.

Example 1: Jack spent 2 hours to write 8 pages of homework. How much can he write in 3 hours?
Solution: Here first find the unit rate.
Jack spends 2 hours to write 8 pages of homework. This can be written as:
Unit rate = 8 pages/ 2 hours = 8/2 pages per hour = 4 pages per hour.
Hence, Number of pages / Time taken = 4.
When the time is 3 hours: Number of pages/ 3 = 4.
This gives number pages = 3 x 4 = 12.
Therefore, Jack writes 12 pages in 3 hours.

Question: Multiple choice question (Pick the correct option.)
What is the unit rate of planting 15 plants in 3 rows? ------ Plants per row?
a)    5          b) 3                 c) 15               d) None of these.