Mental Arithmetic Questions Worksheets - Level 6 Page 2
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21Toys
Advert
The cost of an old toy vehicle depends on its condition and on
You can work out the cost of an advert in a newspaper by using this formula:
whether it is in its original box.
2.
C
is the cost in pounds
Condition
Value
C = 15 + 75
n
n
is the number of words in the advert
excellent, and in its box
100%
good, and in its box
85%
Remember 15n means 15
(a)
An advert has 18 words.
poor, and in its box
50%
multiplied by number of
words in the advert
excellent, but not in its box
65%
Work out the cost of the advert.
Cost = 15 x number of words + 15
good, but not in its box
32%
Cost = (15x 18) + 75
Show your wor
king.
COMMON ERROR
poor, but not in its box
15%
Cost = £270.00 + 75
An incorrect answer
Cost + £345.00
A Mail Van in excellent condition, and in its original box, costs £125.
was to add 18 + 75 to
give an answer of 93.
(a)
How much is a Mail Van in good condition, and in its box?
Pupils not understood
Calculator
100% = £125
the meaning of 15n.
S0
method.
10% = £12.50
15% = £18.75
(£12.50 + £6.25)
85% of 125
5% = £6.25
85%
=
(GOOD CONDITION AND IN BOX)
= 0.85 x 125
£125 - £18.75 = £106.25
(b)
The cost of an advert is £615
= £106 25
This time we are told
•
the final cost is £615.
How many words are in the advert?
(b)
How much is a Mail Van in good condition, but not in its box?
Work in reverse order –
•
inverse
Show your working.
Calculator Method
The last operation in
•
100% = £125
part (a) was + 75, the
32% of £125
inverse is –75
0.32 x £125 = £40
615 – 75 = 540.
•
COMMON ERROR
The inverse of 15n
•
An incorrect answer
(multiply by 15) is divide
was 540. Pupils
A Petrol Tanker in excellent condition, and in its box, costs £152.
(c)
by 15
Another Petrol Tanker should be sold for £98.80
subtracted 75 from
540 ÷ 15 = 36
•
Using the chart above, what is its condition and does it have a
615 and ignored
box?
There are 36 words in
•
division by 15.
the advert
We are looking for a percentage as an answer.
Selling price of petrol tanker = £98.80 x 100%
Original price of petrol tanker £152
This gives an answer of 65%
Using the table at the start of the question the petrol tanker is
EXCELLENT, BUT NOT IN IT’S BOX.
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