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【题目】用7、8、9这三个数字组成两位数乘一位数的算式(数字不得重复),使它们的乘积最大和最小。【分析与解】我们先用7、8、9这三个数字写出所有的两位数乘一位数的算式并算出积:78×9=702,87×9=783,79×8=632,97×8=776,89×7=623,98×7=686。观察上面的算式与积,我们可发现:如果要求乘积为最大,那么一位数应取最大的数,即9,得□□×9;两位数的十位应取剩下数中的较大数,即8,得算式87×9=783。类似的,如果要求乘积为最小,那么一位数应取最小的数,即7,得□□
[Title] with 7,8,9 these three numbers form a two-digit by one-digit formula (numbers can not be repeated), so that their product of the maximum and minimum. 【Analysis and Settlement】 Let’s use the three numbers of 7, 8 and 9 to write out all the two-digit and one-digit formulas and calculate the product: 78 × 9 = 702,87 × 9 = 783,79 × 8 = 632, 97 × 8 = 776, 89 × 7 = 623, 98 × 7 = 686. Observe the above formula and product, we can find: If the required product is the largest, then one digit should take the largest number, that is, 9, was □ □ × 9; two digits of the ten should take the remainder of the more Large number, that is, 8, the formula 87 × 9 = 783. Similarly, if the product is required to be the smallest, then one digit should be the smallest, ie 7,