Mathematics
Grade5
Easy

Question

Ellen wanted to buy the following items: A DVD player for $49.95, a DVD holder for $19.95 and a personal stereo for $21.95. If she has $90 with her, is that enough to buy all these?

  1. Not enough
  2. Enough
  3. Little extra
  4. Exact amount

Hint:

An addition mental math technique is to dissect an addend. This approach might be more effective for some students than left-to-right addition. This method involves dividing up one addend in an equation into more manageable bits. There are certain properties that can be used while calculating which make it easy to add. Here we have given that Ellen wanted to buy the following items: A DVD player for $49.95, a DVD holder for $19.95 and a personal stereo for $21.95. If she has $90 with her, we have to find is that enough to buy all these.
So we will break the number in an appropriate way and then show the sum.

 
 

The correct answer is: Not enough


    Now as we know that here we have to find the step by breaking one number. The fact that there are no steps to memorise is one of the best things about mental math. The "friendly number" addition approach facilitates working with large numbers. This is due to the fact that we are, in essence, decomposing the problem into more manageable components.
    Here we will use some properties which are:
    • Commutative Property of Addition: if a and b are real numbers, then a+b=b+a
    • Associative Property of Addition: if a,b, and c are real numbers, then (a+b)+c=a+(b+c)
    • Compensation Property: It is a mental math strategy for multi-digit addition that involves adjusting one of the addends to make the equation easier to solve.
    Now we have given 49.95 + 19.95 + 21.95, let's solve this.
    49.95 + 19.95 + 21.95
    50 + 20 + 22 = 92 (Rounding the numbers to the nearest whole numbers)
    Since $92 is more than $90, the money she has is not enough to buy things.

    Here the concept of Break Apart Numbers is used where a number is divided in two parts to make addition easy. The concept of friendly numbers is also used so that it becomes easy for addition or subtraction purpose. Since $92 is more than $90, the money she has is not enough to buy things.

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