Question 487330
You need to draw a Venn diagram to solve this.
It's hard to explain without showing you a
drawing, but it looks like 3 interlocking
circles with all 3 circles overlapping in the center.
If you google "Venn diagram" you will see.
The inside of each circle represents the number
of cars in the 3 main categories, 4 cyl, pw, and tsw
4 cyl = 50
pw = 30
tsw = 80
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Where the circles overlap, try to see the regions as:
(1) 4 cyl and pw, but not tsw
(2) 4 cyl and tsw, but not pw
(3) pw and tsw, but not 4 cyl
(4) all 3 features in the center
Try to find the number of cars that fall into 
each of these 4 regions
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First, there are 160 cars, but 65 don't fall into the 3 categories,
so there are 95 cars total
42 have four-cylinder engines and a tilted steering wheel
This is how many fall in the overlap between 4 cyl and tsw
Subtract {{{ 42 - 15 = 27 }}} and you have the region 
(2) 4 cyl and tsw, but not pw
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18 have four-cylinder engines and power windows
Subtract {{{ 18 - 15 = 3 }}}. Now you have the region
(1) 4 cyl and pw, but not tsw
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Look at the region which is pw and nothing else. Call it {{{x}}}
If I add up all the tsw, which is {{{80}}} and {{{ 50 - 42 = 8 }}},
and {{{x}}}, I should get {{{95}}}
{{{ 80 + 5 + 3 + x = 95 }}}
{{{ x = 95 - 88 }}}
{{{ x = 7 }}}
This is pw and nothing else
Now subtract {{{ 30 - 18 - 7 = 5 }}} This is the region
(3) pw and tsw, but not 4 cyl
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Now you can find
Only 4 cyl = {{{ 50 - 3 - 15 - 27 = 5 }}}
Only tsw = {{{ 80 - 27 - 15 - 5 = 33 }}}
Only pw = {{{ 30 - 3 - 15 - 5 = 7 }}}
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Knowing all these regions, you can answer any question, like
How many of these cars have a tilted steering wheel and power windows?
{{{ 15 + 5 = 20}}}
 How many cars have at least one of these features?
{{{ 95}}} have at least one
How many cars have exactly 2 of these features?
{{{ 3 + 27 + 5 = 35 }}}
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Note that is you add up all the 7 regions, you should get {{{95}}}
{{{ 5 + 3 + 15 + 27 + 33 + 5 + 7 = 95 }}}
OK
Hope this helps- at least you're on the right track now