Unsure of what you're asking by "<span>What is the rate of 2.50/10.50 and 1.99/2.50?" Do you mean, "</span><span>What is the RATIO of 2.50/10.50 and 1.99/2.50?"
If so, this ratio is
2.5/10.5 --------------- 1.99/2.50
Invert the denominator, obtaining 2.50/1.99, and then multiply the numerator 2.5/10.5 by this result: