If-else chain of range-checks not executing as expected

When I pass certain float value to compare with my conditional statement it always executes else part.

There are some variables with values:

float total = 74.67 ; 
String grade = "", point = "";

And with this values I want to do this:

if(total>=80){
        grade = "A+";
        point = "4.00";
}else if(total<=79 && total>=75){
        grade = "A";
        point = "3.75";
}else if(total>=70 && total<=74) {
        grade = "A-";
        point = "3.50";
}else if(total<=65 && total>=69){
        grade = "B+";
        point = "3.25";
}else if(total<=64 && total>=60){
        grade = "B";
        point = "3.00";
}else if (total<=59 && total>=55){
        grade = "B-";
        point = "2.75";
}else if (total<=54 && total>=50){
        grade = "C+";
        point = "2.50";
}else if(total<=49 && total>=45){
        grade = "C";
        point = "2.25";
}else if (total<=44 && total>=40){
        grade = "D";
        point = "2.00";
}else {
        grade = "F";
        point = "0.00";
}

but it always shows grade = "F" and point = "0.00".

if I write this,

if(total>=70 && total<=74) {
        grade = "A-";
        point = "3.50";
    }

it shows grade ="" and point ="".

the value of total is showing nicely but there are problem with grade and point. can anyone tell me what is the problem?