Question

Julia wants to bring watermelon for the third grade picnic. Seedless watermelon costs 39 cents for 1/2 kilogram. One serving of watermelon weights about 150 grams. There will be 60 people at the picnic.
a. How many kilograms of watermelon will Julia need to buy?
b. How much will that watermelon cost?

Answer 1

We can model the scenario like this (keep in mind that 150 grams is .15 kilograms):

$\frac{39}{.5} = \frac{x}{60(.15)}$

$\frac{39}{.5} = \frac{x}{9}$

39 cents buys .5 kilograms, x cents buys 9 kilograms (60 servings of .15 kilograms).  We now have our answer for Part A; Julia needs to buy 9 kg of watermelon.  Now, we just have to use cross multiplication to solve for x.

$39*9 = .5x$

$351 = .5x$

$x = 702$

9 kilograms of watermelon cost 702 cents.  702 cents is equivalent to $7.02, so the watermelon will cost $7.02.

Answer 2

One serving:
1 serving = 150g

Find 60 servings:
60 servings = 150 x 60 = 9000g = 9kg

(a) Julia will need to buy 9kg of watermelon.


$\dfrac{1}{2} \text{ kg} \longrightarrow 39 \text{ cents}$

Find 1 kg:
$1 \text{ kg} \longrightarrow 39 \times 2 \text{ cents}$

$1 \text{ kg} \longrightarrow 78 \text{ cents}$

Find 9 kg:
$9 \text{ kg} \longrightarrow 78 \times 9 \text{ cents}$

$9 \text{ kg} \longrightarrow 702 \text{ cents or } \ 7.02$

Answer: The watermelon will cost $7.02