To understand why we learn this concept, let us consider the following situation.
When we are in shop, we find two deal as follows :
(i) 500 g of detergent costing $3.50
(ii) 750 g detergent costing $5.40
decide which is the better deal.
To properly compare prices, we need to convert the cost of an item into a rate called unit rate.
Consider the following grocery items and decide which is the better value for money:
Question 1 :
Answer :
By choosing small box,
Cost of 300 g of corn flakes = $2.15
= 215 cents
Cost of 1 gram = 215/300
= 0.716 cents
By choosing large box,
Cost of 500 g of corn flakes = $3.29
= 329 cents
Cost of 1 gram = 329/500
= 0.658 cents
0.716 > 0.658
So, choosing 500 g corn flakes is better deal.
Question 2 :
Answer :
By choosing 6 pack,
Cost of 6 towels = $2.99
= 299 cents
Cost of 1 towel = 299/6
= 49.83
By choosing 4 pack,
Cost of 4 towels = $1.79
= 179 cents
Cost of 1 towel = 179/4
= 44.75
49.83 > 44.75
So, choosing 4 pack is better deal.
Question 3 :
Answer :
By choosing 2 liters can
Cost of 2 liters of milk = $3.89
= 389 cents
Cost of 1 liter of milk = 389/2
= 194.5 cents
Dividing by 100
Cost of 1 liter of milk = $1.945
By choosing 600 ml can
Cost of 600 ml milk = $2.19
= 219 cents
Cost of 1 ml of milk = 219/600
Cost of 1000 ml milk (or) Cost of 1 liter milk
= (219/600)⋅1000
= 365 cents
Dividing by 100
Cost of 1 liter of milk = $3.65
3.65 > 1.945
So, choosing 2 L milk can is the better deal.
Question 4 :
Answer :
By choosing 10 m pack
Cost of 10 meter ribbon = $4.20
= 420 cents
Cost of 1 meter ribbon = 420/10
= 42 cents
Dividing by 100
Cost of 1 meter ribbon = $ 0.42
By choosing 8 m pack
Cost of 8 meter ribbon = $3.60
= 360 cents
Cost of 1 meter ribbon = 360/8
= 45 cents
Dividing by 100
Cost of 1 meter ribbon = $ 0.45
0.42 < 0.45
So, choosing 10 meter ribbon is the better deal.
Question 5 :
Answer :
By choosing 5 liter can
Cost of 5 liter paint = $65
Cost of 1 liter paint = 65/5
= $13
By choosing 2 liter can
Cost of 2 liter paint = $31
Cost of 1 liter paint = 31/2
= $15.50
13 < 15.50
So, choosing 5 liter can is the better deal.
Question 6 :
Answer :
By choosing 25 kg pack
Cost of 25 kg potatoes = $35
Cost of 1 kg potato = 35/25
= $1.4
By choosing 10 kg pack
Cost of 10 kg potatoes = $16.50
Cost of 1 kg potato = 16.50/10
= $1.650
1.650 > 1.4
So, choosing 20 kg potato is the better deal.
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