We are used to working with one-digit divisors. As long as we know our multiplication tables, it's easy for us to figure out the answer to division problems. But what if the divisor has two digits? With two digits, we go beyond the multiplication tables. What are the multiples of 21 or 58? It will take a lot of time if we have to write a whole new multiplication table for double-digit numbers. If we use estimation, we can save a lot of time.
Let's see how estimation works in this problem:
Here, we divide the whole number 318 by 77. It would take too long to solve for all the multiples of 77, so let's try looking at the numbers in a different way.
77 = 7 tens and 7 ones
318 = 31 tens and 8 ones
How many tens are there in 77? There are 7 tens. How many tens are there in 318? There are 31 tens. We don't need to look at the ones digits. All we need are the tens values. The next step is to divide 31 by 7:
The closest multiple to 31 that can be divided by 7 is 28. Twenty-eight divided by seven equals 4 (28 ÷ 7 = 4). Now let's go back to the original problem and write 4 above the 8 in the ones place.
To check, we multiply 77 times 4.
We write the answer, 308, below 318 in the division problem. Take away 308 from 318, and you are left with 10. This is the remainder of the problem.
Don't be alarmed when you find greater (larger) numbers both in the dividend and the divisor. Using estimation will save you a lot of time trying to find the answer.
