请教七月JJ两道[转自我看机经]

smart

6. A retailor bought 100 radios for $30 each, sold n radios for $50 each, and sold the left for x bucks each,  made a total profit of $1500,  then ask about whether x > $40 or not? (A)
    (1) n > 6
    (2) n < 8

7. A researcher was doing an experienment, and got 84 numbers of data and their sum correctly, but divided the sum by a wrong number x (other than 84) and got the average 400, ask whether we could figure out the correct averageD)
    (1) The wrong number x is 77
    (2) If the sum were divided by 66, the average would be 88

smart

[转帖]6. 我的答案是B 因为 （50-30)*n + (x-30)(100-n) =1500 得到 50（90-n)/(100-n) = x 若要x>40, 则 50（90-n)/(100-n) >40 得到 n < 50 所以当且仅当 n<50时，x>40. (1) n>6, 不定 (2) n<8, 肯定成立 7. 假设S是correct sum, x*400=S=84*average 只要知道x, 就可求出正确的average (1) x =77 成立 (2) 66*88 = x*400 成立