Question 20
The teacher writes the digits 8,7,6,5,4,3,2,1 in this order. Students may insert only addition signs between the digits, without changing their order.
Example: $8+7+65+4+3+21=108$.
How many ways of inserting addition signs give a total of 90?
Example: $8+7+65+4+3+21=108$.
How many ways of inserting addition signs give a total of 90?