Of 100 clock radios with digital tuners andor CD players sol

Of 100 clock radios with digital tuners and/or CD players sold recently in a department store, 70 had digital tuners and 90 had CD players. How many radios had both digital tuners and CD players?

Solution

Let x radios have both digital tuners and CD players

So, clock radios with only digital tuners = 70 -x

clock radios with only CD players = 90 -x

Total clock radios : ( 70 -x) +(90 -x) + x = 100

160 - 2x +x = 100

160 -x =100

x = 160 -100 = 60 radios have both digital tuners and CD players