SOURCE

// 根据的数反求随机计算式 加减法
function getEquation(amount = 2, max = 20) {
    res = Math.round(Math.random() * 20)
    // 运算符
    var operators = ['+', '-'];
    var arr = [res];
    for (var i = 1; i < amount; i++) {
        // 获取随机运算符
        var operator = operators[Math.round(Math.random() * 1)];
        var a, b;
        if (operator == '+') {
            b = Math.round(Math.random() * arr[0]);
            a = arr[0] - b;
        } else {
            b = Math.round(Math.random() * (max - arr[0]));
            a = arr[0] + b;
        }
        arr.shift();
        arr = [a, operator, b].concat(arr);
    }
    return {
        eq: arr.join(' '),
        res: res
    }
}

for (var i = 1; i <= 50; i++) {
    var equation = getEquation(Math.round(Math.random() * 1) + 2);
    $('<p>' + equation.eq + ' = </p>').appendTo('body');
}


// console.log(JSON.stringify())

body{
    padding: 3.5rem 1.5rem;
    width: 210mm;
    /* font-size: 1.75rem;  */
    column-count: 3;
    background-color: #fff;
}