Calculating matters

Here, why we can't solve it as :12. 60 * (0. 5*1. 1)? I am facing some difficulty in understanding of proportions calculating. Why is the idle time 100/90? I need detailed explanation, please. Thank you

Sir, in order not to waste time, I wanted to add, I understand that for every 1 hour, 10 % is lost. But I want to get this idea of difference between 100/90 and just multiplying by 1. 1. As this might be applied to other cases.

For every 100 hours paid, 10% is idle and therefore 90 hours are actually worked. Putting it the other way round, for every 90 hours worked, 10 hours will have been idle, and therefore 100 hours will have been paid.

oh now it's clear. It's not for every one hour of 90 hours we add 10 % (which would be 0. 9) but 10 hours are divided over those 90 which is 0. 111111..... Thank you.

You are welcome :-)