Hey Rohana,
In view that there are 3Q here, I will only post the solutions to Q1, Q2 here first while the remaining one will be posted in due course.
<Updates>
25/2 - Corrected answer for Q2
25/2 - Q3 solution was posted
Following pls find my worked solutions:
Q1
Apply <Age Difference> concept - where age difference between 2 persons remains constant / same now and then.
<1st When statement>
K |---|---|
B |---|
M |<--- 30 --->|
Age Diff (between K,B ) = 2p - 1p = 1p
Age Diff (between M,K) = 30 - 2p
<2nd When statement>
K |------------|
B |<- 21 ->|
M |------------|------------|
Age Diff (between K,B ) = 1u - 21
Age Diff (between M,K) = 2u - 1u = 1u
We now have ...
Age Diff (between K,B ):
1p = 1u - 21
1u - 1p = 21 -- (1)
Age Diff (between M,K):
30 - 2p = 1u
1u + 2p = 30 -- (2)
Using <Simultaneous Eqn> method, eliminate <1u> from (1),(2).
(2)-(1):
2p + 1p --> 9
3p --> 9
1p --> 3
B = 1p --> 3, when M = 30
Age Diff (between M,B ) = M - B = 30 - 3 = 27
When M = 62, B = 62 - 27 = 35 yrs old
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Q2.
4F = 3S
5F - 2S = 750 -- (1)
4F - 3S = 0 -- (2)
(1)-(2):
F + S = 750
Given that 1u of F and 1u of S cost $30, we have ...
3000 ÷ 750 = 4
i.e. 4F + 4S = 3000
Hence, 1u of F = 4
=========================
Q3
<Value>
T |----|<- 64 ->|
C |----|
Total spending: 124
124 - 64 = 60
2u --> 60
1u --> 30
Hence, T = 1u + 64 --> 30 + 64 = 94
C = 1u --> 30
<Qty>
C |---|---|---|
T |---|
1u of T = $94
1u of C = 30 ÷ 3 = $10
Difference in amount between same qty of T and C = 94 - 10 = $84
Given that T - C = $8.40, the amount diff above for the same qty/number of T and C purchased is a result of this.
Hence, 84 ÷ 8.4 = 10
This means there were 10 T and 10 C in that <1u> qty of T and C.
Qty of C (purchased) = 3u --> 3 × 10 = 30
Amount spent on C = $30
Hence, cost of 1C = 30 ÷ 30 = $1
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Trust this helps.
Do let me know again if this is different from your Answerkey or if there are further clarifications.
Cheers,
Edward