Written algorithms for subtraction Equal additions algorithm - explanation using 74 - 38 This algorithm is based on the principle that adding an equal number to the subtrahend and the minuend does not alter the subtraction. So the strategy is to add 10 to both numbers. Thinking text Algorithm 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. Back to Teaching algorithms of subtraction