Math.
posted by Unknown. .
There are 420 calories in 2 1/4 cans of grape soda. How many calories are in 1 can of soda?

420cal = 2.25 cans
? cal = 1can
To find the number of calories we just do the cross product, so:
420cal x 1can / 2.25cans = ? cal
420cal/2.25cans = 186.6667cal 
you have to divide 420 by 2 1/4,, to do this, you must first convert 2 1/4 into improper fraction:
2 1/4 = 9/4
*note that to convert mixed number into improper fraction, multiply the denominator (which is 4) by the whole number (which is 2), then add the numerator (which is 1), thus 4*2 + 1 = 9, but the denominator is still 4, thus it's 9/4,,
then divide:
420 / (9/4)
*to do this, get the reciprocal of 9/4, that is, interchange numerator and denominator:
9/4 > reciprocal is 4/9
now, the operation becomes multiplication instead of division:
420 * (4/9) = ?
you simplify this.
so there,, :) 
Thank you Ivan and Jai.