How do you can use mental math to compare 7 lb to 120 oz

There are 16 oz in one pound. Just mentally multiply 7 by 16. A trick for doing this is multiplying 7 x 10, then adding it to the product of 7 x 6. Together, they'll be the product of 7 x 16. You'll get 70 + 42. Those added together is 112. Then, you can easily see that 120 is bigger than 112. Hope this helps you, and good luck!