求教该GMAT题目的意思和解答方法~Ofthethree-digitintegersgreaterthan700,howmanyhavetwodigitsthatareequaltoeachotherandtheremainingdigitdifferentfromtheothertwo?a/90b/82c/80d/45e/36

Question

求教该GMAT题目的意思和解答方法~
Of the three-digit integers greater than 700 ,how many have two digits that are equal to each other and the remaining digit different from the other two?
a/ 90
b/ 82
c/ 80
d/ 45
e/ 36

Answer 1

C
百位只能是7、8、9三种.
为7时,个位=十位 有8个数字（0-9除了0和9）；百位=十位=7,有9个；百位=个位,9个.
为8时,按照上面所列,分别为9、9、9
为9时,分别为9、9、9
因此,一共8+9*8=80