In place value notation, 9 tens and 10 ones together are equal to which number?

Introduction / Context:
Understanding expressions like 9 tens and 10 ones helps to build a strong foundation in place value. These expressions describe a number in terms of groups of tens and individual ones. Translating such descriptions into standard numerical form is a basic but important skill in arithmetic reasoning.

Given Data / Assumptions:
- We have 9 tens.
- We also have 10 ones.
- We must combine these to find the total number in standard numeric form.

Concept / Approach:
A ten represents 10 units, and a one represents 1 unit. So 9 tens means 9 * 10, and 10 ones means 10 * 1. Adding these values gives the total number. Sometimes, after addition, regrouping may show that the number of ones can be converted into more tens.

Step-by-Step Solution:
Step 1: Convert tens to units. 9 tens = 9 * 10 = 90 units. Step 2: Convert ones to units. 10 ones = 10 * 1 = 10 units. Step 3: Add the units: 90 + 10 = 100 units. Step 4: Therefore, 9 tens and 10 ones together equal 100.

Verification / Alternative Check:
You can also think of 9 tens and 10 ones as 9 tens plus 1 ten and 0 ones, because 10 ones equal 1 ten. Thus, you get 10 tens, which is 100. This confirms the result in another way and shows how regrouping works in the place value system.

Why Other Options Are Wrong:
Option A (910) comes from concatenating 9 and 10 as digits rather than adding their place values.
Option B (90) counts only the tens and ignores the ones.
Option C (91) would correspond to 9 tens and 1 one, not 9 tens and 10 ones.

Common Pitfalls:
Learners sometimes read tens and ones as separate digits and write them side by side, instead of converting them to total units. To avoid this, always translate phrases like 9 tens and 10 ones into multiplication and addition, then simplify.

Final Answer:
The expression 9 tens and 10 ones equals 100.