Irfan had 900 magnets of which 25% were star-shaped magnets. How many star-shaped magnets must he buy to increase the number of star-shaped magnets in his collection to 55%?

Answer 1

Out of 900 magnets, 25% are star-shaped, or 0.25 x 900 = <<0.25*900=225>>225 magnets.
To increase the percentage of star-shaped magnets to 55%, the total number of magnets must be multiplied by 55/100 = 0.55.
So Irfan needs a total of 900 x 0.55 = <<900*0.55=495>>495 magnets in his collection.
He already has 225 star-shaped magnets, so he needs to buy an additional 495 - 225 = <<495-225=270>>270 star-shaped magnets. Answer: \boxed{270}.