In this problem, #$90=100#, therefore we need to find #30%# and subtract it from the original to get the discount price of #70%# of the original. An easy way to find #30%# is to find #10%# by dividing the original amount by #100#, then multiplying by #3#.
#100%=$90#
As #100/10=10#, we can divide by #100# to find #10%#
#90/10=$9#
Therefore #10%=9#
As we want to find #30%#, we need to find out how many times #10# goes into #30#
#30/10=3# Therefore we need to multiply the #10%# we found by #3#
#$9 xx 3=$27# This is therefore #30%# of the original amount.
If you wanted the amount of the discount, the answer is #color(red)($27)#
But this isn't it, we found #30%# but we want #70%# of the original amount, so we minus the answer we have from the original:
#$90-$27=$63#
This is like saying
#100%-30%=70%# which is the value we want.
#therefore# discounted price=#color(red)($63#
If you wanted the price after discount the answer is #$63#
