Answer:
42
Explanation:
A shares a bag of sweets with her friends.
She gives B 2/5 of the sweets.
She gives C 3/10 of the sweets. (I'll assume you mean 3/10 of total 1 and not 3/10 of the remaining 3/5.)
She has 18 sweets left.
How many sweets does A give to B?
She gave away 2/5+3/10 of the sweets, meaning she kept 1- (2/5+3/10) = 1-(4/10+3/10) = 1-7/10 = 3/10, which is what she has left.
Let x equal the total number of sweets in the bag originally.
3/10 x = 18
Multiply by 10/3
x=18*10/3 = 6*10 = 60 sweets
She gave away 7/10 of 60 = 7 * 6 = 42 sweets