js浮点数运算（加法、乘法）

let a = 0.1
      let b = 0.2
      let sum = a + b

      let sum1 = (a * 10 + b * 10) / 10
      console.log(sum, sum1)
      const sum2 = 111.1 * 12
    const sum3 = 111.1 * 100 * 12 / 100
    console.log(sum2, sum3)