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1, 10, 100 Less
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Foundational Skills
Identify digit change (1 less)
\[ \text{Which changes in } 346? \rightarrow 6 \]
Identify the specific digit that changes when finding 1 less.
Identify digit change (10 less)
\[ \text{Which changes in } 425? \rightarrow 2 \]
Identify the specific digit that changes when finding 10 less.
Identify digit change (100 less)
\[ \text{Which changes in } 2536? \rightarrow 5 \]
Identify the specific digit that changes when finding 100 less.
1 Less
1 less than 1-digit
\[ \text{1 less than } 7 \rightarrow 6 \]
Simple subtraction from a single digit.
1 less than 2-digit
\[ \text{1 less than } 45 \rightarrow 44 \]
Simple subtraction (no boundary).
1 less than 3-digit
\[ \text{1 less than } 346 \rightarrow 345 \]
Simple subtraction (no boundary).
1 less than 4-digit
\[ \text{1 less than } 2847 \rightarrow 2846 \]
Simple subtraction (no boundary).
1 less (crossing tens)
\[ \text{1 less than } 40 \rightarrow 39 \]
Crossing a tens boundary (e.g., 40 to 39).
1 less (3-digit, cross tens)
\[ \text{1 less than } 150 \rightarrow 149 \]
Crossing tens boundary in 3-digit numbers.
1 less (4-digit, cross tens)
\[ \text{1 less than } 3270 \rightarrow 3269 \]
Crossing tens boundary in 4-digit numbers.
1 less (cross hundreds)
\[ \text{1 less than } 300 \rightarrow 299 \]
Crossing a hundreds boundary.
1 less (4-digit, cross 100s)
\[ \text{1 less than } 2500 \rightarrow 2499 \]
Crossing a hundreds boundary in 4-digit numbers.
1 less (cross thousands)
\[ \text{1 less than } 4000 \rightarrow 3999 \]
Crossing a thousands boundary.
10 Less
10 less than 2-digit
\[ \text{10 less than } 53 \rightarrow 43 \]
Simple subtraction of 10.
10 less than 3-digit
\[ \text{10 less than } 425 \rightarrow 415 \]
Simple subtraction of 10.
10 less than 4-digit
\[ \text{10 less than } 3254 \rightarrow 3244 \]
Simple subtraction of 10.
10 less than 11-19
\[ \text{10 less than } 17 \rightarrow 7 \]
Result becomes a single digit.
10 less (cross hundreds)
\[ \text{10 less than } 305 \rightarrow 295 \]
Crossing a hundreds boundary (tens is 0).
10 less (4-digit, cross 100s)
\[ \text{10 less than } 2503 \rightarrow 2493 \]
Crossing a hundreds boundary (tens is 0).
10 less (cross thousands)
\[ \text{10 less than } 105 \rightarrow 95 \]
Crossing thousands boundary to 2 digits.
10 less (4-digit, cross 1000s)
\[ \text{10 less than } 5003 \rightarrow 4993 \]
Crossing thousands boundary (tens/hundreds 0).
10 less (cross 10,000s)
\[ \text{10 less than } 1005 \rightarrow 995 \]
Crossing ten-thousands boundary.
100 Less
100 less than 3-digit
\[ \text{100 less than } 345 \rightarrow 245 \]
Simple subtraction of 100.
100 less than 4-digit
\[ \text{100 less than } 4256 \rightarrow 4156 \]
Simple subtraction of 100.
100 less (cross thousands)
\[ \text{100 less than } 145 \rightarrow 45 \]
Crossing thousands boundary to 2 digits.
100 less (4-digit, cross 1000s)
\[ \text{100 less than } 3056 \rightarrow 2956 \]
Crossing thousands boundary (hundreds is 0).
100 less (cross 10,000s)
\[ \text{100 less than } 1045 \rightarrow 945 \]
Crossing ten-thousands boundary.
Special Cases
1 less than power of 10
\[ \text{1 less than } 1000 \rightarrow 999 \]
Special case where all digits change.
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