You can **multiply or divide both** value and percentage. 510 minutes is 510·60=30600 seconds:
|Value|Percentage||
|:-|:-|:-|
|30600 seconds|100%|divide both by 30600|
|1 second|0.003%|multiply both by 61|
|61 seconds|0.199%|so that's 99.801% remaining|
|1 second|0.003%|multiply both by 25|
|25 seconds|0.082%|so that's 99.918% remaining|
|1 second|0.003%|multiply both by 36|
|36 seconds|0.118%||