X/x+9 (original fraction)
x+1/ x+10 = 4/13
x+1=4 so x=3 and x+10=13 so again x=3
now that you have the value of x, substitute it into the original fraction to get:
3/12
These problems really aren't hard just set them equal to each other and see if what they are saying is true. Are they equal? Do they both equal 0?
To do it without a calculator:
10% of 67 is 6.7
6.7 x 8 is 53.6 (80%)
1% of 67 is .67
53.6 - .67 is 52.93 (79%)
20/5 = 4
therefore the unit price for the bottles of juice is 4
