For every rational number a/b, a ≠ 0, there exists a rational number c/d such that (a/b) x (c/d) = 1. Then c/d is called the multiplicative inverse of a/b.
That is, if (a/b) is a rational number, then (b/a) is the multiplicative inverse or reciprocal of it.
Multiplicative inverse of 2 is 1/2 and that of -3/5 is -5/3.
1 and – 1 are the only rational numbers which are multiplicative inverses to themselves.
That is,
multiplicative inverse of 1 = 1
multiplicative inverse of -1 = -1
0 has no multiplicative inverse or multiplicative inverse of 0 is undefined.
Example 1 :
Find the multiplicative inverse of 9/11.
Solution :
Multiplicative inverse of 9/11 = 11/9
Example 2 :
Find the multiplicative inverse of -5.
Solution :
Multiplicative inverse of -5 = -1/5
Example 3 :
Find the multiplicative inverse of 2⅗.
Solution :
Convert the given mixed number to an improper fraction.
2⅗ = 13/5
Reciprocal of 13/5 is 5/13.
Multiplicative inverse of 2⅗ = 5/13
Example 4 :
What is the multiplicative inverse of the sum of 3/4 and 5/6?
Solution :
Two fractions 3/4 and 5/6 have different denominators.
Least common multiple of (4, 6) = 12.
Make the denominator of each fraction as 12 using multiplication.
3/4 = (3 x 3)/(4 x 3) = 9/12
5/6 = (5 x 2)/(6 x 5) = 10/12
3/4 + 5/6 :
= 9/12 + 10/12
= (9 + 10)/12
= 19/12
Reciprocal of 19/12 is 12/19.
Multiplicative inverse of (3/4 + 5/6) = 12/19
Example 5 :
What is the multiplicative inverse of (5/21) x (7/20)?
Solution :
= (5/21) x (7/20)
Simplify.
= (1/3) x (1/4)
= 1/12
Reciprocal of 1/12 is 12.
Multiplicative inverse of (5/21) x (7/20) = 12
Example 6 :
What is the multiplicative inverse of (24/7 ÷ 32/35)?
Solution :
= 24/7 ÷ 32/35
Simplify.
= 24/7 x 35/32
= 3/1 x 5/4
= 15/4
Reciprocal of 15/4 is 4/15.
Multiplicative inverse of (24/7 ÷ 32/35) = 4/15
Example 7 :
What is the multiplicative inverse of 0.32?
Solution :
0.32 = 32/100
= 8/25
Reciprocal of 8/25 is 25/8.
25/8 = 3.125
Multiplicative inverse of 0.32 = 3.125
Example 8 :
What is the multiplicative inverse of 1.25?
Solution :
1.25 = 125/100
= 5/4
Reciprocal of 5/4 is 4/5.
4/5 = 0.8
Multiplicative inverse of 1.25 = 0.8
Example 9 :
If y/3 and 4/5 are multiplicative inverse to each other, then find the value of y.
Solution :
Since y/3 and 4/5 are multiplicative inverse to each other, their product is equal to 1.
y/3 x 4/5 = 1
4y/15 = 1
Multiply each side by 15/4.
y = 15/4
Example 10 :
If 2/5 and 7/z are multiplicative inverse to each other, then find the value of z.
Solution :
Since 2/5 and 7/z are multiplicative inverse to each other, their product is equal to 1.
2/5 x 7/z = 1
14/5z = 1
Take reciprocal on each side.
5z/14 = 1
Multiply each side by 14/5.
z = 14/5
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