HOME

Course Chapters

Section Tests

Useful Materials

Glossary

Online Calculators

Credits

## Problem 1 Solution

What are the results of the following calculations?
a.
4 + 5 * 10 -3^2
b.
(1+24/3)^2
c.
(-2)^2
d.
-2^2

```(a) 45     (b) 81     (c) 4      (d) -4

```

### Solution Steps for Part (a):

The key: What is the order of operations?

1. Scan the expression to be evaluated and note that there are no parentheses that need to be evaluated first. There is, however, an exponentiation, 3^2, which can be read "3 to the power 2" or "3 squared". Evaluate this and replace 3^2 by 9. The expression is now: 4 + 5 * 10 - 9
2. Scan the expression and note any multiplications or divisions, and evaluate those pairwise operations, replacing the expression with the result. There is only one, 5 * 10, which we evaluate and replace with 50. The expression is now: 4 + 50 - 9
3. Scanning the expression now, we see we only have additions and subtractions left, which we can evaluate left to right. 4 + 50 gives 54, and subtracting 9 we get 45. The answer is 45.
Note: If you had evaluated the expression "left to right" to begin with, you would have gotten 4 + 5 is 9, times 10 is 90, minus 3 is 87, squared is 7569! Not even close to the accepted answer of 45.

### Solution Steps for Part (b):

The key: What is the order of operations?

1. Scan the expression and note there are parentheses, the "insides" of which must be evaluated first. Within these parentheses, there is a division which must be performed first. Replacing 24/3 by 8, we now have: (1+8)^2
2. We still have the parentheses, so we perform the addition inside the parentheses next, replacing 1 + 8 with 9. Our expression is now: (9)^2 or simply 9^2
3. This expression can be read as "nine squared" or "nine raised to the power two" so the answer is 81.

### Solution Steps for Part (c):

The key: What is the order of operations?

1. Scan the expression and note there are parentheses, the "insides" of which must be evaluated first. So it is "minus 2" which must be raised to the power 2.
2. Evaluating the expression, we get 4. Remember, a negative times a negative gives a positive, so any negative number multiplied by itself gives a positive result.

### Solution Steps for Part (d):

The key: What is the order of operations?

Scanning the expression, we note there are no parentheses to indicate that the minus "goes with" the 2, so the first operation is "2 raised to the power 2" or "2 squared" which is 4. Replacing 2^2 by 4, the answer is -4.

Note: it is a very common mistake to confuse the expressions in problems 1 (c) and 1 (d) as being the same. The parentheses make a big difference.

Next Try It Out Problem.

Developed by
Shodor
in cooperation with the Department of Chemistry,
The University of North Carolina at Chapel Hill