78 can be regrouped into 6 tens and 18 ones.
8 tens and 4 one
yes
(3*10)+(9*1)=39
With addition, you need to regroup in the event that there are more than 10 ones or 10 tens. In a subtraction, you must regroup whenever there are insufficient ones or tens to subtract.
8 tens.
6+6 7+7 10+8 6+4
500+10+6 = 516
10+6
9 rounds up to 10. You can't put ten tenths in one place, you need to regroup and increase the ones by one.
Ten of them because 10*1 = 10
One ten is equal to ten ones
10 ones equall 1 ten