If my job after school pays me double minimum wage, but my boss says he needs to cut my pay by 10% but will give me 10% more hours to make up for it, will i still make the same amount of money?

No, you'll do 10% more work, and you'll make 1% less money.

Let's imagine that he cut your hourly rate in half, and doubled your hours.
Then you would be doing twice as much work, for exactly the same money.

He told you right at the beginning what he's doing, where he said he needs to
cut your pay.  Right there, you knew that he's not going to offer you any way to
make the same amount of money. 

What he offered you is a way for him to get more work done, in return for slightly
less money.  And from YOUR point of view ... you spend 10% more time on the
job, you get home 10% later, you're 10% more tired, you have 10% less time for
homework, and you lose a penny of every dollar that you're making now.

The boss is a scheming rat for concocting such a deal.  If you take it, you're being
screwed three ways.

Don't let him tell you that he's doing you a favor, and you should be grateful to him
for the job.  He is a businessman, and you should act like one too. You have a
product that you're willing to sell, for a fair price. Your product is your work.  The
boss needs your product. 

Back when you first started working for him, the two of you agreed on a price for
your product.  There's no good reason that he should expect to keep getting the
same product, but at a new reduced price.

Remember when you started that job.  That was a time when he didn't know
how well you would be able to do it, so he wanted your product at an "introductory
trial reduced price".  At the same time, you were happy to get the job, so you were
willing to work for smaller pay at the beginning.  But now that he's become
satisfied with your work and your attitude, and you've learned to do the job better
than before ... NOW your product should be worth more than before, not less.

Increase your hours ? ! ? Thanks a bunch, boss !  Work is not a product that sells
at a quantity discount.

5/ 1/3=15 i think sorry if im wrong