Q. 345.0( 8 Votes )

# Form the pair of

Answer :

i) Let the number of boys and girls be ‘a’ and ‘b’.

10 students of class X took part in Mathematics quiz. If the number of girls is 4 more than the number of boys

⇒ a + b = 10 and b = a + 4

Thus, a = 3 and b = 7

ii ) Let the cost of 1 pen be a and 1 pencil be b.

5 pencils and 7 pens together cost Rs. 50, whereas 7 pencils and 5 pens together cost Rs. 46

⇒ 7a + 5b = 50 and 5a + 7b = 46

Solving by multiplying 1^{st} by 7 and 2^{nd} by 5 and subtracting

⇒ 24a = 120

⇒ a = Rs. 5

Thus, 35 + 5b = 50

⇒ b = Rs. 3

iii) Let the number of pants and skirts bought be ‘a’ and ‘b’

Champa went to a ‘sale’ to purchase some pants and skirts. When her friends asked her how many of each she had bought, she answered, “The number of skirts is two less than twice the number of pants purchased. Also, the number of skirts is four less than four times the number of pants purchased.”

⇒ b = 2a – 2 and b = 4a – 4

⇒ 2a – 2 = 4a – 4

⇒ a = 1

Thus, b = 2 – 2 = 0

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