只有 3 和 5（每个重复至少一次）的最大 3 位数是多少？
在我们的日常生活中，我们使用数字。它们通常被称为数字。我们无法计算物体、日期、时间、金钱或任何没有数字的东西。这些数字有时用于测量，有时用于标记。数字具有允许它们对它们进行算术运算的功能。这些数字用数字和文字表示。例如，3 写成 3，33 写成 33，以此类推。为了进一步学习，学生可以练习用文字写出 1 到 100 的数字。
我们在数学中学习了各种类型的数字。自然数和整数、奇数和偶数、有理数和无理数等等都是例子。在本文中，我们将介绍所有不同的品种。除此之外，这些数字还用于各种应用，包括数字系列、算术表等。
- A number is an arithmetic value that is used to represent and calculate a quantity. Numbers are represented by numerals, which are written symbols such as “2.”
- A number system is a method of writing numbers that uses logical digits or symbols to represent them.
数字类型
数字系统是将数字分类为集合的系统。在数学中，有几种不同类型的数字：
- 自然数：自然数是从 1 到无穷大的正整数，其中包含从 1 到无穷大的正整数。自然数集合用字母“N”表示，由N = 1, 2, 3, 4, 5,…………
- 整数：非负整数，通常称为整数，是不包含任何小数或小数部分的非负整数。它用字母“W”表示，整数集合包含W = 0, 1, 2, 3, 4, 5,…………
- 整数：整数是所有整数的集合，但它们也包括一组负自然数。整数用字母“Z”表示，整数的集合是 Z = -3, -2, -1, 0, 1, 2, 3。
- 实数：实数都是不包含虚数的正整数和负整数、小数和小数。字母“R”用于表示它。
- 有理数：有理数是可以表示为一个数与另一个数的比率的任何数。任何可以写成 p/q 形式的数字都符合条件。有理数用符号“Q”表示。
- 无理数：无理数是不能表示为一个与另一个的比率的数字，用字母 P 表示。
- 复数：复数 (C) 是可以用 a+bi 形式表示的数字，其中“a”和“b”是实数，I 是虚数。
Places in a number: If a number is 12345 then 5 is at units place, 4 is at tens place, 3 is at hundredth place, 2 is at thousand place, and so on…….
So, a number can be written as :
1*(Digit at ones place) + 10*(Digit at tens place) + 100*(Digit at hundreds place)+………………….
只有 3 和 5（每个重复至少一次）的最大 3 位数是多少？
解决方案：
Three-digit numbers start from 100, 101, 102,…………. to 999.
We have to find the number with digits only 3 and 5 so there can be cases like:
- Use 3 and 5 both at least once.
- Use only 3 and 5
Case 1: As 999 is the largest three-digit number but we have to use 3 and 5 at-least once.
So, we can put 5 and 3 at tens and ones place respectively.
So, the number will be 953.
If we put 3 at tens place and 5 at ones place the number will be 935 which is smaller than 953.
So, 953 is the largest 3-digit number with 3 and 5 (using at-least once).
Case 2: As 999 is the largest three-digit number but we have to use 3 and 5 only. So, we can put 5 at hundred and tens place and 3 at units place. So, the number will be 553.
类似问题
问题 1：只有 7 和 8 的最大 3 位数是多少？
解决方案：
Three-digit numbers start from 100, 101, 102,…………. to 999.
We have to find the number with digits only 7 and 8 so there can be cases like :
- Use 7 and 8 both at least once.
- Use only 7 and 8 (Both at-least once )
Case-1: As 999 is the largest three-digit number but we have to use 7 and 8 at-least once.So, we can put 8 and 7 at tens and ones place respectively. So, the number will be 987.
If we put 7 at tens place and 8 at ones place the number will be 978 which is smaller than 987.
So, 987 is the largest 3-digit number with 7 and 9 (using at-least once).
Case-2: As 999 is the largest three-digit number but we have to use 7 and 8 only. So, we can put 8 at hundred and tens place and 7 at units place. So, the number will be 887.
问题 2：只有 1 和 9 的最大两位数是多少？
解决方案：
Two-digit numbers start from 10, 11, 12,…………. to 99.
We have to find the number with digits only 1 and 9 so there can be cases like :
- Use 1 and 9 both at least once.
- Use only 1 and 9
For 2-digits number, both cases are same:
As 99 is the largest two-digit number but we have to use 1 and 9 at-least once.So, we can put 9 and 1 at tens and ones place respectively. So, the number will be 91.
If we put 1 at tens place and 9 at ones place the number will be 19 which is smaller than 91.
So, 91 is the largest 2-digit number with only 1 and 9 (using at-least once).