the last one because 7*3=21 14*3=42 and 21*3=63
There were 40 advance tickets sold, and 30 same-day tickets sold.
Roberto overtakes Juanita at the rate of (7.7 mi)/(11 h) = 0.7 mi/h. This is the difference in their speeds. The sum of their speeds is (7.7 mi)/1 h) = 7.7 mi/h.
Roberto walks at the rate (7.7 + 0.7)/2 = 4.2 mi/h.
Juanita walks at the rate 4.2 - 0.7 = 3.5 mi/h.
_____
In a "sum and diference" problem, one solution is half the total of the sum and difference. If we let R and J be the respective speeds of Roberto and Juanita, we have
R + J = total speed
R - J = difference speed
Adding these two equations, we have
2R = (total speed + difference speed)
R = (total speed + difference speed)2 . . . . . as computed above
Hey there!!
How do we solve this problem :
We will use the combinations formula to solve this :
c ( n , r ) where n = 11 and r = 2
c ( n , r ) = n ! / r ! ( n - r ) !
... 11 ! / 2 ! ( 11 - 2 ) !
... 11! / 2! × 9!
... 11! / 2 × 9!
... 11×10×9×8×7×6×5×4×3×2 / 2×9×8×7×6×5×4×3×2
... 11×10 / 2
... 11 × 5
... 55 combinations.
Hence, the required answer = 55 , option ( d )
Hope my answer helps!
