Javier has a balance of $1,800.50 in his personal checking account. He pays two bills out of this account: a $150.70 electric bill, and a $70.80 cell phone bill. The amount left with Javier after paying the bills =  ________________

The correct answer is: $1579

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 150.70 + 70.80, let's solve this.
150.70 + 70.80
Solving the decimal part first, we get:
0.70 + 0.80 = 1.50
150 + 70 = 220
220 + 1.50 = 221.50
1800.50 – 221.50 = 1579
So, the amount left is $1579.

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. So, the amount left is $1579.