70 is decomposed into 60 10 10-8=2. The answer is 62.

54 is decomposed into 40 14 14-7=7. The answer is 47.

This is to decompose the minuend into two integer tens, subtract one and add the remaining integer tens.

It can also be calculated as 70-(10) = (60) 54-(10) = (44).

(60)+(2)=(62) (44)+(3)=(47)

This is to treat a number as an integer ten, subtract more and add more.