एक संख्या और उसके एक-तिहाई का अंतर 520 है। उस संख्या का 20% कितना होगा?

A person saves 90% of his income. If his expenditure is ₹520, find his income (in ₹).

By how much is 30% of 60 greater than 25% of 40?

By how much is 30% of 50 greater than 35% of 30?