Question 1111309
450*0.2 =  90 
450-90 = 360
or you can take this short cut:
450*0.8 = 360
now add the sales tax, again you can take a short cut:
360*1.06 = 381.60
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how do the short cuts work? 20% is 20 percent, and per-cent means for every hundred. To make our calculations easy, we divide the percentage by 100:
20/100 = 0.2 now we have that 20% is the same as 0.2 of 1. 1 is the primal number, every natural number except 0 is made up of 1s. So now it's easy to calculate the 20% of any number, just multiply times 0.2
Likewise with the tax, it's 6% and 6/100 = 0.06, now add 0.06 + 1 and multiply it to any number you choose to add 6% to the number.