Use compatible numbers to estimate each product and quotient.
23*1/2
1/3*11

Lets consider 17*1/2 first. Since 17 is between 16 and 18, 17*1/2 is between 16*1/2 and 18*1/2, that is 17*1/2 is between 8 and 9.

Likewise if the problem is 29*1/2 then 29 is between 28 and 30 so 29*1/2 is between 28*1/2 = 14 and 30*1/2 = 15.

If the problem is 22*1/3 then you need to find two numbers that are divisible by 3, one smaller than 22 and one larger than 22. Since 22 is between 21 and 24, 22*1/3 is between 21*1/3 = 7 and 24*1/3 = 8.

Now try 23*1/2 and 11*1/3.