シェルスクリプトのif-else文と浮動小数点数の比較

だから私は成績入力を受け、各セクションの重みに基づいて成績を計算するスクリプトを書いてきました。最後に計算された成績に基づいて文字評価を出力します。私のコードはif-else文まで問題ありませんが、各if-else文の条件で誤った数値エラーが発生し始めます。

#!/bin/sh
#Calculate weighted grade and output grade letter

echo "What is your total Lab/Assignments grade?"
read labGrade
echo "What is your Midterm grade?"
read midtermGrade
echo "What is your total Quizzes grade?"
read quizGrade
echo "What is your Final Exam grade?"
read finalGrade

weightedLab=`echo "0.25*$labGrade" | bc`
weightedMidterm=`echo "0.30*$midtermGrade" | bc`
weightedQuiz=`echo "0.15*$quizGrade" | bc`
weightedFinal=`echo "0.30*$finalGrade" | bc`

totalGrade=`echo "$weightedLab + $weightedMidterm + $weightedQuiz + $weightedFinal" | bc`

if [ $totalGrade -ge 90.00 ]
then
        echo "Your total grade is an A+!"
elif [ $totalGrade -ge 85.00 -a $totalGrade -le 89.00 ]
then
        echo "Your total grade is an A!"
elif [ $totalGrade -ge 80.00 -a $totalGrade -le 84.00 ]
then
       echo "Your total grade is an A-!"
elif [ $totalGrade -ge 76.00 -a $totalGrade -le 79.00 ]
then
        echo "Your total grade is a B+"
elif [ $totalGrade -ge 72.00 -a $totalGrade -le 75.00 ]
then
        echo "Your total grade is a B"
elif [ $totalGrade -ge 68.00 -a $totalGrade -le 71.00 ]
then
        echo "Your total grade is a B-"
elif [ $totalGrade -ge 64.00 -a $totalGrade -le 67.00 ]
then
        echo "Your total grade is a C+"
elif [ $totalGrade -ge 60.00 -a $totalGrade -le 63.00 ]
then
        echo "Your total grade is a C"
elif [ $totalGrade -ge 56.00 -a $totalGrade -le 59.00 ]
then
        echo "Your total grade is a C-"
elif [ $totalGrade -ge 50.00 -a $totalGrade -le 55.00 ]
then
        echo "Your total grade is a D"
else
        echo "Your total grade is an F"
fi

What is your total Lab/Assignments grade?
100
What is your Midterm grade?
100
What is your total Quizzes grade?
100
What is your Final Exam grade?
90
./A2.sh: 20: [: Illegal number: 97.00
./A2.sh: 23: [: Illegal number: 97.00
./A2.sh: 26: [: Illegal number: 97.00
./A2.sh: 29: [: Illegal number: 97.00
./A2.sh: 32: [: Illegal number: 97.00
./A2.sh: 35: [: Illegal number: 97.00
./A2.sh: 38: [: Illegal number: 97.00
./A2.sh: 41: [: Illegal number: 97.00
./A2.sh: 44: [: Illegal number: 97.00
./A2.sh: 47: [: Illegal number: 97.00
Your total grade is an F

この値を正しく比較するには、コードをどのように変更する必要がありますか？