Algebra 1 Common Core Student Edition, Grade 8-9

H o w is f in d in g

odds d ifferen t from

finding probability?

To find odds, you

compare favorable and

unfavorable outcomes.

To find probability, you

compare favorable

outcomes and all

possible outcomes.

H o w is t h e f o r m u la
for experim ental
probability similar
to the form ula
for theoretical
probability?
In each formula, you
divide a number of items
corresponding to an
event by a total number
of items.

Odds describe th e likelihood of an event as a ratio com paring the n u m b e r of favorable

an d unfavorable outcom es.

odds in favor of an event = number of favorable outcomes

number of unfavorable outcomes

o dds against an event = ^ m b e r of unfavorable outcomes

number of favorable outcomes

Pr o b l em 3 Fi n d i n g O d d s

What are the odds in favor o f the spinner landing on a num ber

greater than or equal to 6?

Favorable outcomes: 6 , 7, 8 Total: 3

Unfavorable outcom es: 1, 2, 3,4, 5 Total: 5

The odds in favor of th e event are | , or 3 : 5.

Go t It? 3. W hat are th e o dds against th e sp in n er landing on

a n u m b e r less th a n 3?

Experimental probability is b ase d on d ata collected from re p eated trials.

experim ental probability P(event) number of times the event occurs

number of times the experiment is done

Fi n d i n g Ex p e r i m e n t a l P r o b a b i l i t y

Quality Control After receiving com plaints, a skateboard manufacturer inspects

1000 skateboards at random. The manufacturer finds no defects in 992 skateboards.

What is the probability that a skateboard selected at random has no defects? Write

the probability as a percent.

PC I I HU LlC lC Llo I j r t \ number of skateboards with no defectsi r i *i

v J number of skateboards examined

~ 992 1000 Substitute.

= 0.992 Write as a decimal.

= 99.2% Change to percent.

The probability th a t a skateboard selected at ra n d o m has no defects is 99.2%.

£ Got It? 4. Suppose th e m an u fa ctu rer in P roblem 4 inspects 2500 skateboards.

There are 2450 skateboards w ith no defects. W hat is th e probability

th at a skateboard selected at ra n d o m h as no defects? W rite the

probability as a percent.

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