Answer:
The number of knitted scarves is 10 
 The number of knitted mitten is 20 
Step-by-step explanation:
Given as :
The cost of each knitted scarves = $50
The cost of pairs of mittens = $25
Total number of scarves and mitten bought = 30
The total money invested to pay for items = $1000
Let The number of knitted scarves = k
Let The number of mitten = m
<u>Now, According to question</u>
The total money invested to pay for items = cost of each knitted scarves × number of knitted scarves + cost of pairs of mittens × number of mitten 
i.e $1000 = $50 × k + $25 × m
Or, 40 = 2 k + m
i.e 2 k + m = 40           ........A
And
Total number of scarves and mitten bought =  number of knitted scarves +  number of mitten 
i.e k + m = 30            ...........B
Now, solving eq A and eq B
So, (2 k + m ) - ( k + m ) = 40 - 30
Or, (2 k - k) + ( m - m) = 10
Or, k + 0 = 10
∴  k = 10
So,  The number of knitted scarves = k = 10
Put the value of k into eq B
∵ k + m = 30
So, m = 30 - k 
or, m = 30 - 10
∴  m = 20
 The number of knitted mitten = m = 20
Hence,  The number of knitted scarves is 10 and The number of knitted mitten is 20  . Answer