identity used is
x³ + y³+ z³– 3xyz = (x + y + z) (x² + y² + z² – xy – yz – zx).
then use
(x+y+z)² = x²+y²+z²+2(xy+yz+xz)
225= 83 + 2(xy+yz+xz)
xy+yz+xz = (225-83)/2
xy+yz+xz= 142/2
xy+yz+xz= 71
ok
now use identity
x³ + y³+ z³– 3xyz = (x + y + z) (x² + y² + z² – xy – yz – zx).
now
x³ + y³+ z³– 3xyz = 15 (83 – xy – yz – zx).
= 15[83 - (71)]
= 15×12
=180
If she studied for 2.3 she would have a total of 11.5 because if she got 5 points per hour you just have to multiply it the number of hours she spent studying. So 2.3 x 5 = 11.5! :-)
What did each friend pay, where c is the cost of the trip, not including the tip.
1 / 3 ( c+7.00)=11.25
Multiply both sides by 3
c + 7 = 33.75
Subtract 7 from both sides
c = 26.75
Multiples: 15, 30, 45, 60, 75. 5/80 or 1/16
