Fred completed 10 math problems. this is 40%of the number of math problems he has to do. how many math problems does he have to do?

He need to do is like 24 math problems because 10 math problem are 40 plus another 10 math problem is 80 plus 20 equal a 100

40 times 2 equals 80. So if we double both the numbers now he has done 20 math problems and 80% is done. But now we have to split the 10 in half because you cant do 80% plus 40% You have to do 80% plus 20% and that would be half of the 10. So in conclusion your answer is 25 math problems.; )