Mathematics

Grade6

Easy

Question

# Four gallons of gasoline costs $16.80. The cost of 15 gallons would be ________.

- 60
- 63
- 50
- 53

Hint:

### We are given the cost of 4 gallons of gasoline. It is $16.80. We have to find the cost of 15 gallons of the gasoline. We are also told that rate is constant. To solve the question, we will first find the rate using the first data. Once we find the rate, we will use it to find the required quantity.

## The correct answer is: 63

### Let’s denote number of gallons by N.

The given values of number of gallons of gasoline and cost are as follows.

N = 4

Cost = $16.80

We have to find the cost of 15 gallons. We will find the rate first. We will find rate by taking the ratio of cost to the number of gallons. As rate is constant, we will use it to find the cost of 15 gallons.

Let’s see the equation

We will use this value to find the cost of 15 gallons

Let’s see the equation

We will rearrange the expression for N. We will multiply L.H.S and R.H.S by N.

Rate × N = Cost

Cost = Rate × N

= 4.2 × 15

= 63 dollars

Therefore, the cost of 15 gallons is 63 dollars.

The other method is to take the ratios and directly equate them. As the rate is constant, so the ratios will be constant. So we will consider the quantity we have to find as x and then equate the ratios. It will be a shortcut.