Description:
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Casting to an int where a subtraction equals 0.2, when multiplied by 10 and cast to an int returns a value of 1. If the subtraction equals 0.3 then the result of the above cast will equal 3

Test script:
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$kwatts = ((int)(($row[7]Â  - $row[4]) * 10))/10 ;
   with $row[7] = 55.40
   with $row[4] = 55.20
but returning a $kwatts value of 0.1

php > $a = 0.1;
php > $b = 0.3;
php > echo $b - $a ;
0.2
php > echo ($b - $a)* 10 ;
2
php > echo(int)($b - $a)* 10 ;
0
php > echo(int)(($b - $a)* 10) ;
1
php > echo(int)(10 * ($b - $a)) ;
1
php > echo(int)((10 * ($b - $a))) ;
1