Multiplying rational numbers word problems :
To solve many real world problems, we may have the situation of multiplying rational numbers. Here we are going to see how multiplying rational numbers can be used to solve real world problems.
Example 1 :
A student can eat 1/8 of a pizza. If there are 40 students in David's class, how many pizzas does David need ?
Solution :
To find how many pizzas that David needs, we have to multiply 40 and 1/8.
Step 1 : Multiply 40 by 1/8
40 x 1/8
Step 2 : Simplify
5 x 1/1
Step 3 : Multiply
5 x 1/1 = 5
Hence, David needs 5 pizzas.
Example 2 :
There are 450 students in school. If 4/9 th of the students are boys, find the number girls in the school.
Solution :
If 4/9 of the students are boys, then 5/9 th of the students are girls. Because 9 - 4 = 5.
To find number of girls, we have to multiply 450 by 5/9.
Step 1 : Multiply 450 by 5/9
450 x 5/9
Step 2 : Simplify
50 x 5/1
Step 3 : Multiply
50 x 5/1 = 250
Hence, there are 250 girls in the school.
Example 3 :
The science teacher is filling her new fish aquarium. The aquarium holds 40 gallons. If she fills the aquarium 4/5 of the way full, how many gallons will she need?
Solution :
If 4/5 of the aquarium is filled, then 1/5 th of the aquarium to be filled to make it full. Because 5 - 4 = 1.
To find number of gallons, we have to multiply 40 by 1/5.
Step 1 : Multiply 40 by 1/5
40 x 1/5
Step 2 : Simplify
8 x 1/1
Step 3 : Multiply
8 x 1/1 = 8
Hence, the science teacher needs 8 gallons to make the aquarium full.
Example 4 :
A baker needs to make 8 batches of cookies for a party. If each batch requires 2 3/4 cups of flour, how many cups will he need ?
Solution :
To find number of cups needed, we have to multiply 8 by 2 3/4.
Step 1 : Multiply 8 by 2 3/4
8 x 2 3/4
Step 2 : Simplify
8 x 11/4 = 2 x 11/1
Step 3 : Multiply
2 x 11/1 = 22
Hence, the baker needs 22 cups of flour to make 8 batches of cookies.
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