$ 10 coupons are free for 30 salads.
Step-by-step explanation:
Given,
$ 1 coupon is free for every 3 salads.
To find the least number of salads should buy to get $ 10 in coupons.
$ 1 coupon is free for 3 salads.
$ 2 coupons is free for 6 salads.
$ 3 coupons is free for 9 salads.
Following this the general formula we get,
$ n coupons is free for 3n salads. where n= 1,2,3..
Now, putting n=10 we get,
$ 10 coupons are free for 3×10 = 30 salads.
