IB Mathematics SL Prep

Category - IB Mathematics

Sawyer’s Pet Store has averaged a net profit of $2,500 for the past 11 weeks. What is the total net profit over this length of time?
  1. $26,000
  2. $27,500
  3. $27,900
  4. $28,000
  5. $29,300
Explanation
Answer: $27,500. It is very easy to quickly multiply 2-digit numbers by 11. For this problem, let’s calculate 25 x 11, then add the 2 zeroes back at the end later.

Key Takeaway: To multiply a number by 11:

Rewrite the first number with a space between. In this case, 2__ 5. Then, add those two numbers together (to get 7), and put that in the space: 275. Therefore, 25 x 11 is 275. Going back to the original problem, add the zeroes back at the end. 2500 x 11 = 27,500.

If the sum of the two digits is greater than 9, you will have to carry the 1. For instance, 48 x 11.

4_8
4+8 = 12.

Put the 2 in middle and carry the 1 and you will get 528.
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