Question 34703
Here is a good formula for ALL percentage problems like these:
{{{ is/of = percent/100 }}}
Using this ... let's solve:


(1)    what number is 15% of 135
{{{ x/135 = 15/100 }}}
Cross multiply ...
{{{ 100x = 135(15) }}}
divide by 100
{{{ x = (135(15))/100 }}}
Reduce and Multiply and divide
{{{ x = (135(3))/20 }}}
{{{ x = (27(3))/4 }}}
{{{ x = 81/4 }}}
{{{ x = 20.25 }}}


(2)   3 is what percent of 87?
{{{ 3/87 = x/100 }}}
{{{ 87x = 3(100) }}}
{{{ x = (3(100))/87 }}}
{{{ x = 300/87 }}}
{{{ x = 3.45 rounded }}}


(3) 19.6 is 28% percent of what number?
{{{ 19.6/x = 28/100 }}}
{{{ 19.6/x = 7/25 }}}
{{{ 7x = 25(19.6) }}}
{{{ x = (25(19.6))/7 }}}
{{{ x = 490/7 }}}
{{{ x = 70 }}}