Solution - Long multiplication
Step-by-step explanation
1. Rewrite the numbers from top to bottom aligned to the right
| Place value | tens | ones | . | tenths |
| 1 | 0 | . | 5 | |
| × | 4 | |||
Ignore the decimal points and multiply as if these are whole numbers (as if each most right digit is the ones digit):
In this case we removed 1 decimal place(s). So once calculated, the result will be reduced by the factor of 10.
| Place value | hundreds | tens | ones |
| 1 | 0 | 5 | |
| × | 4 | ||
2. Multiply the numbers using long multiplication method
Start by multiplying the ones digit (4) of the multiplier 4 by each digit of the multiplicand 105, from right to left.
Multiply the ones digit (4) of the multiplicator by the number in the ones place value:
4×5=20
Write 0 in the ones place.
Because the result is greater than 9, carry the 2 to the tens place.
| Place value | hundreds | tens | ones |
| 2 | |||
| 1 | 0 | 5 | |
| × | 4 | ||
| 0 |
Multiply the ones digit (4) of the multiplicator by the number in the tens place value and add the carried number (2):
4×0+2=2
Write 2 in the tens place.
| Place value | hundreds | tens | ones |
| 2 | |||
| 1 | 0 | 5 | |
| × | 4 | ||
| 2 | 0 |
Multiply the ones digit (4) of the multiplicator by the number in the hundreds place value:
4×1=4
Write 4 in the hundreds place.
| Place value | hundreds | tens | ones |
| 2 | |||
| 1 | 0 | 5 | |
| × | 4 | ||
| 4 | 2 | 0 |
Because we have 1 digit(s) to the right of the decimal point in the numbers that are being multiplied, we move the decimal point 1 time(s) to the left (reducing the result by the factor of 10) to get the final result:
The solution is: 42
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