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A written description of equal addition

This algorithm is based on the principle that adding an equal number to the subtrahend (38 in this case) and the minuend (74 in this case) does not alter the difference. So the strategy is to add 10 to both numbers, but IN TWO DIFFERENT WAYS.

The icon for equal additions on the main page illustrates this principle: the difference in height between Gary and Dianne is the same, whether they are standing on the ground or they both step up onto a platform.

Try to subtract the ones first. We cannot take away 8 ones from 4 ones. Add 10 ones to the 4 ones in 74 giving 14 ones.

tens ones

Add 1 ten to the 3 tens in 38 giving 4 tens. Note that 10 ones is 1 ten, so we have added the same number to 74 and to 38.

Tens ones

The difference between 7 tens 14 ones and 4 tens 8 ones is the same as the difference between 7 tens 4 ones and 3 tens 8 ones. 14 ones take away 8 ones is 6 ones.

Tens ones

Now subtract the tens. 7 tens take away 4 tens is 3 tens.

Tens ones

74 take away 38 is 36.

Instead of carrying out the subtraction of 38 from 74, we have actually done the subtraction of FORTY EIGHT from SEVENTY FOURTEEN.