Nicholas bought 5 pens for $3 at this rate how much will he spend on 8 pens

First, you would want to find the price of 1 pen, since 5 pens doesn't go into 8 pens evenly. To do this, you would have to divide 5 pens and $3 by 5, because remember, whatever you do to one side, do to the other. Anyways, 5 pens divided by 5 is 1 pen, and $3 divided by 5 is $0.60, so the price of one pen is 60 cents. To find the price of 8 pens, multiply $0.60 by 8. That gives you $4.80, so the price for 8 pens is $4.80. 

Divide 3 by 5 to find the price of each one and then multiply it by 8 to find how many for 8

Iwould say they are complementary because that’s the division of a 90 degree angle and it’s split between the middle of them