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Subtract a 1-digit number from a 2-digit number

Subtraction is understood as finding the difference between a two-digit whole number and a one-digit whole number by reasoning with tens and ones; when the ones are insufficient, one ten is decomposed into ten ones without changing the number’s value. A number line, place-value representation, or related addition equation can show the relationship and help avoid treating the digits as independent quantities. This scope is limited to minuends from 10–99 and subtrahends from 0–9, not multi-digit subtrahends, decimals, or more advanced general algorithms.

Detailed Explanation: Subtract a 1-digit number from a 2-digit number

To subtract a 1-digit number from a 2-digit number, think about the tens and ones.

Example: Find (42−7)(42-7).

  1. Write (42)(42) as 44 tens and 22 ones:
42=40+2 42=40+2
  1. There are only 22 ones, so we cannot take away 77 ones. Decompose 11 ten into (10)(10) ones:
42=3 tens+12 ones 42=3\text{ tens}+12\text{ ones}
  1. Subtract 77 ones from (12)(12) ones:
12−7=5 12-7=5
  1. There are 33 tens left, so the answer is:
3 tens+5 ones=35 3\text{ tens}+5\text{ ones}=35

Therefore,

42−7=35\boxed{42-7=35}

You can check by adding:

35+7=4235+7=42

Learn by doing: Subtract a 1-digit number from a 2-digit number

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    Subtraction - Whole Number 2 x 1, With Borrow

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