A boy saves Rs 1.75 per day. Find the least number of days in which he will be able to convert his savings into multiple of Rs. 10 note.

?

Suppose it takes n days for boy to earn in multiple of 10 .Let the total amount he earn be 10x .  Here x will be always an integer .

Now , n × 1.75 = x × 10 

⇒ n × 1.75/100 = x

⇒ n × 7/40 = x 

so for x to be integer , n should me multiple of 40 . 

So the minimum number of days will be 40 . 

Hope this would have cleared your doubt .