How to Ace Standardized Tests: What Must Be in the Ones Place?

This post is part of a series of standardized test prep posts.

Here is a really simple trick that lets you quickly eliminate wrong answers on multiple choice multiplication tests!

Check just the ones digits in the problem.  Multiply quickly in your head, and you will know what the ones digit must be in the correct answer.  Cross off answers that don’t have the correct ones digit.

For example, if you are multiplying 57 X 48, you know that 7 X 8 = 56 (multiplying the ones digits of both numbers).  The ones digit is 6.  So the correct answer to the problem MUST have 6 as the ones digit.

Save a lot of time by trying your new skill before you solve a multiplication problem on a standardized test!

Example: 486 X 592 = ____
a. 7,776
b. 287,712
c. 289,525
d. 64,293

Strategy: What must be in the ones place?

#1: The answer MUST be an EVEN number, because both numbers are EVEN (I teach my students they can look at just the number in the ones place to determine if a number is even or odd). Cross off answers c and d because they are odd numbers.

#2: The answer MUST END in 2, because 6 X 2 = 12, which puts 2 in the ones place. Cross off answer a because 6 is in the ones place.

Result: Only answer b can be correct.

There! You have the correct answer without taking the time to solve a complex long multiplication problem! You also can use the method “What Must Be in the Ones Place?” to quickly eliminate wrong answers to multiple choice problems using other operations: addition, subtraction and division.

Posted in Academics,Math by Corey Green @ Apr 29, 2011

 

2 Comments »

  1. This is why i don’t like multiple choice tests. I’m convinced that multiple choice tests are given for two reasons: 1) The results appear to be comparible from one student to another. 2) They’re easy to grade, and therefore cheap.

    However, i’m not convinced that multiple choice tests can test for competence. Ever. No work is shown. So how can they?

    Now, teaching the multiplication trick is good for checking your answers. And, even if you have a calculator, you should check your answers. But using the check as the answer? That’s not competence in math. That’s competence in test taking. The real world is not, in general, a multiple choice test. And i fear setting up anyone for failure.

    The results are not, in fact, comparible from one student to another, except in how good they are at taking tests.

    Comment by Stephen — May 18, 2011 @ 10:27 AM

  2. I prep students so they feel confident before taking multiple choice tests. Remember, they take more than math tests in that format! While learning in the classroom, we work the old-fashioned way: show your work. Third graders are busy learning multiplication tables and we get to long multiplication at the end of the year. Students don’t use calculators to check their work — we go over problems they missed and I show them where an error occurred. Thank you for commenting.

    Comment by Corey Green — May 18, 2011 @ 11:38 AM

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