A taxi-driver, filled his car petrol tank with 40 litres of petrol on Monday. The next day, he filled the tank with 50 litres of petrol. If the petrol costs Rs.44 per litre, how much did he spend in all on petrol?
Petrol filled on Monday =40 litres
Petrol filled on the next day (Tuesday) =50 litres
Cost of 1 litre of petrol =Rs. 44
Now, the amount spent in overall petrol =Rs. (44×(40+50))
=44×90
=44×(100−10)
Since, Distributive property over subtraction:
a×(b−c)=(a×b)−(a×c)
⇒44×(100−10)
=44×100−44×10
=4400–440
=3960
Therefore, he spent Rs. 3960 on petrol.