Infinitely many.
Choose any number X such that 0 < X < sqrt(20) and let Y = 20/X.
Then X*Y = X*20/X = 20 and since X was selected arbitrarily, there are infinitely many possible answers to the question.
20 nickles
about 8
10 ways.10 ways.10 ways.10 ways.
how many ways to make 25p using 1p 2p 5p 10p 20 coins
It depends on the currency and so the coinage. For example, there are 20 (Euro) cent coins but not 20 US cents.
1 x 20 = 20 2 x 10 = 20 4 x 5 = 20
20 nickles
1*20, 2*10, 4*5.
40
20 pennies, 4 nickles, and 2 dimes. 3 ways.
There are infinitely many answers. Let A be any whole number and let B = -A -20 Then by the closure of integers, B must be a whole number. And A + B = A + (-A - 20) = -20 Since A is arbitrary, there are infinitely many ways of choosing A and so there are infinitely many ways in which two whole numbers will make -20.
There are 41 ways.
about 8
10 ways.10 ways.10 ways.10 ways.
20 + 8 = 28p
how many ways to make 25p using 1p 2p 5p 10p 20 coins
There are not 20 ways - there are only 12.