If you want to calculate on time go to tempotoets.nl
Also try how good you are at mental arithmetic!
Here you learn arithmetic error-free for FREE
Here you can exercise fractions.
Suppose the sunm 1/2 + 1/3 than the answer is 5/6. You fill in 5/6.
If you choose 1-5 than the fractions are additions. The denominators are not larger than 5
If the aswer is 5/4 than you don't have to rewrite the answer to 1 1/4