Idea 20of 22Builds onThe parts make 100%
Out of the number asked
Which number goes on the bottom when you sampled a big school?
Today you'll discover
- why the bottom number is the number asked
- what the population's size is for
- the slip of dividing by everyone
Think first20 of the school's 240 were asked
9 of the 20 asked want pizza. The school has 240. Which fraction is pizza's?
Decide first, then press Next. Read the line under the question: how many were asked?
A table for “Which lunch should we add?”: 20 of the school's 240 students were asked. Pizza 9, tacos 6, soup 3, salad 2, total 20. Then fractions over 20: 9/20, 6/20, 3/20, 2/20, and percents: 45%, 30%, 15%, 10%, with 100% on the total row.
See the whole ideathe big idea and the key word, in one place
The big idea
The denominator is the number asked, not the whole population: 9 of 20 is 9/20.
Easy to get wrongDividing by the whole school, 9/240, treats the 220 who were never asked as if they had said no.
Where it goes nextTo predict for the school, keep the share: 45% of the 20 asked suggests about 45% of all 240.
Key word
- denominator
- the bottom number of a fraction; in a relative frequency, the number asked
Ready to use it?
- Find a relative frequency out of the number asked, not the population.