Answer:
2.5 ounces of 20% glucose and 2. 5 ounces of water should be used to prepare 10% glucose.
Step-by-step explanation:
 Given = Required
 C1xV1 = C2xV2
 20 x V1 = 10 x 5 
 V1 = (10 x 5) / 20
 = 2.5 ounces of 20% glucose
Dilution factor = total amount - V1 (amount of given)
 = 5 - 2.5
 = 2.5 ounces
Take 2.5 ounces of 20% glucose and make up the total amount upto 5 ounces by adding 2.5 ounces of water.
Also simply as the percentage concentration is reduced by half so 1:2 dilution is used which means 2.5 ounces of 20% glucose with 2.5 ounces of water will give total of 5 aunces of solution
2.5: 5 = 1:2