Question

3，7，8，9用加减乘除怎样能得出24

Answer 1

（9+7-8）*3=24
当然还有个作弊的通解，不过这个用了导数和阶乘，不符合只用加减乘除的要求

Answer 2

根据题意可知。
算式就是。
3×（7+9-8）＝3×8＝24，
一般是利用四六或三八二十四。

Answer 3

3，7，8，9用加减乘除怎样能得出24？
答：9-8=1
1+7=8
3×8=24
总体为：3×（9-8+7）=24

Answer 4

3×[9-8+7]=24.

Answer 5

3 * (7 - 8 + 9)
下面是js代码:
<h4>3，7，8，9用加减乘除怎样能得出24?</h4>
<input type="text" id="text"/>
<script>
document.getElementById("text").value = "ssssss";

// a b c d
function seekExpression0() {
console.log('seekExpression0------------------------------>seekExpression0');
var a = 3, b = 7, c = 8, d = 9;
var jia = '+', jian = '-', cheng = '*', chu = '/';
var operater = [jia, jian, cheng, chu];
var expression = '';
for (var i = 0; i < 4; i++) {
var op0 = operater[i];
for (var j = 0; j < 4; j++) {
var op1 = operater[j];
for (var k = 0; k < 4; k++) {
var op2 = operater[k];
expression = 'a ' + op0 + ' b ' + op1 + ' c ' + op2 + ' d';
var jieguo = eval(expression) * 1;
console.log('expression:' + expression + ' = ' + jieguo);
console.log('');
if (jieguo === 24) {
return expression;
}
}
}
}

return 'NotFoundTheExpressiong';
}

// (a b) c d
// a (b c) d
// a b (c d)
// (a b c) d
// a (b c d)
function seekExpression1(bracketPosition) {
console.log('seekExpression1------------------------------>' + bracketPosition);
var a = 3, b = 7, c = 8, d = 9;
var jia = '+', jian = '-', cheng = '*', chu = '/';
var operater = [jia, jian, cheng, chu];
var expression = '';
for (var i = 0; i < 4; i++) {
var op0 = operater[i];
for (var j = 0; j < 4; j++) {
var op1 = operater[j];
for (var k = 0; k < 4; k++) {
var op2 = operater[k];
// (a b) c d
if (bracketPosition == 1) expression = '(a ' + op0 + ' b) ' + op1 + ' c ' + op2 + ' d';
// a (b c) d
if (bracketPosition == 2) expression = 'a ' + op0 + ' (b ' + op1 + ' c) ' + op2 + ' d';
// a b (c d)
if (bracketPosition == 3) expression = 'a ' + op0 + ' b ' + op1 + ' (c ' + op2 + ' d)';
// (a b c) d
if (bracketPosition == 4) expression = '(a ' + op0 + ' b ' + op1 + ' c) ' + op2 + ' d';
// a (b c d)
if (bracketPosition == 5) expression = 'a ' + op0 + ' (b ' + op1 + ' c ' + op2 + ' d)';
//
var jieguo = eval(expression) * 1;
console.log('expression:' + expression + ' = ' + jieguo);
console.log('');
if (jieguo === 24) {
return expression;
}
}
}
}
return 'NotFoundTheExpressiong';
}

var expressionOk = seekExpression0();
var bracketPosition = 1;
while (expressionOk == 'NotFoundTheExpressiong' && bracketPosition <= 5) {
expressionOk = seekExpression1(bracketPosition);
bracketPosition++;
}
console.log('expressionOk:' + expressionOk);
document.getElementById("text").value = expressionOk;

</script>