While on a ski vacation, a group can rent pairs of skis and snowboards by the week thy get a reduce rate if they rent 7 pairs of skis for every 3 snowboards

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They get a reduced rate if they rent 7 pairs of skis for every 3 snowboards rented the reduced ski rate is $45.50 per pair of skis per week, and the reduced snowboard rate is $110 per snowboard per week. the sales tax on each rental is 16%The group has $2500 available to spend on ski and snowboard rentals. Why is the greatest number of pairs of skis and snowboards the group can rent if the ratio of pair of skis to snowboards is 7:3?

7 pairs of skis * 45.50 rent per pair = 318.50
3 snowboards * 110 rent per snowboard  =  330

318.50 + 330 = 648.50
648.50 * 1.16 = 752.26

2500 / 752.26 = 3.32 or 3 sets of 7:3 ratio.

7 * 3 = 21 
21 * 45.50 = 955.50

3 * 3 = 9
9 * 110 = 990

955.50 + 990 = 1,945.50 
1,945.50 * 1.16 = 2,256.78 total cost 

2,500 - 2,256.78 = 243.22 change

The group can rent 21 pairs of skis and 9 snowboards for only 2,256.78