Alright so to do this you need some basic algebra you have to pay an extra 20% of whatever you buy thus we can make the following equation .2x+x=20 (since 20 is the amount of money you have) combining the like terms, 1.2x=20 and finally, dividing both sides by 1.2 x=$16.67 don't forget to check! .05*16.67=.83 (sales tax makes the total $17.5) .15*16.67=2.5 (tip makes the total $20) whaddya you know, it works! most expensive item you can buy will cost $16.67 hope this helped!
