Pg 631 (563) - Q2
Notice that the average 60 is also one of the 3 numbers. Since 50 is 10 less than 60, the third number needs to be 10 more than 60 in order for the average to be 60. The third number is therefore 70. You can also do it the long way by assigning the third number to be “x” and solving for it with (50 + 60 + x)/3 = 60 to get x = 70.