(a)
Find the sum of 3985 and 1273.
Notice that the word sum requires you to add the numbers together.
Begin by estimating the answer.
4000 + 1000 = 5000
so the answer should be a little more than 5000
Write one number above the other.
Add the digits in the ones column.
Add the digits in the tens column, writing the 1 above the next column.
Add the digits in the hundreds column, including the extra 1.
Add the digits in the thousands column, including the extra 1.
Check the final answer is similar to your estimate.
5258
(b)
Find the difference between 506 and 28.
Notice that the word difference requires you to subtract the second number from the first.
Begin by estimating the answer.
500 – 30 = 470
so the answer should be about 470
Write one number above the other, be careful to line up the columns correctly.
6 – 8 would be negative, so we need to borrow from the next column.
However the next column is 0, so we will borrow from the column to the left of it.
This turns the 0 into a 10.
We can then borrow from the tens column.
So we can now find 16 – 8 for the ones column.
For the second column (tens) we can do 9 – 2 = 7 and finally in the hundreds column, 4 – 0 = 4.
Check that your answer is similar to your estimate.
478
(c)
Without using your calculator, calculate 32.5 – 1.74.
You must show all your working.
Begin by estimating the answer.
32.5 is about 33 and 1.74 is about 2
33 – 2 = 31
So the answer should be about 31
Write one number above the other, be careful to line up the columns correctly, putting the decimal point in a column of its own and filling in the spaces with zeros.
Consider the hundredths column; 0 – 4 is negative, so we need to borrow from the next column.
Consider the tenths column, 4 – 7 would be negative, so we need to borrow from the next column.
We can now do 14 – 7 = 7, and continue subtracting in the other columns.
Remember to put the decimal point in line in the answer with those in the question.
Check that this is similar to your original estimate.
30.76
So, 3516 × 23 = 80 868
So, 3516 × 7 = 24 612
1 × 23 = 23
2 × 23 = 46
4 × 23 = 92
8 × 23 =184
103 644 is less than 120 000, but it has the same place value so it is likely to be correct.
2879 × 36 = 103 644
eg. 534 ÷ 6
So, 534 ÷ 6 = 89
568 ÷ 8 = 71