He'll save 3 dollars if he buys 60 mouth guards in packs of 10 which is 6×14.50 = 87
Whereas
4×22.50 = 90
Answer:
(5/7 - 1) * (2/3 + (1/6 - 1/9) * 18/5 + 1/15) - (2/7 + 1/3) * (-7/13)
= (5/7 - 7/7) * (2/3 + (3/18 - 2/18) * 18/5 + 1/15) - (6/21 + 7/21) * (-7/13)
= (-2/7) * (2/3 + 1/18 * 18/5 + 1/15) - 13/21 * (-7/13)
= (-2/7) * (2/3 + 1/5 + 1/15) + 7/21
= (-2/7) * (10/15 + 3/15 + 1/15) + 1/3
= (-2/7) * 14/15 + 1/3
= -4/15 + 1/3
= -4/15 + 5/15
= 1/15