06 Kunci Jawaban dan Pembahasan MAT IX

4. Jawaban: a
Un = 2n(n – 1)
U8 = 2 × 8 × (8 – 1) = 16 × 7 = 112
U7 = 2 × 7 × (7 – 1) = 14 × 6 = 84
U8 – U7 = 112 – 84 = 28
5. Jawaban: b
48 : (–6) – 5 × (–3) = –8 + 15
= 7
6. Jawaban: c
Suhu daging = –8°C + 82°C – 36°C
= 74°C – 36°C
= 38°C
7. Jawaban: b
Bunga 4 bulan = Rp40.000,00.
Bunga 1 tahun = 12
× Rp40.000,00
4
= Rp120.000,00
bunga 1tahun
% bunga per tahun = × 100%
modal
= 120.000
× 100% = 6%
2.000.000
8. Jawaban: a
Luas tanah = 2 3
4 hektare
Luas tanah yang ditanami jeruk
= 2
5
× 2 3
4
= 2
5
× 11
4
= 22
20 hektare
Luas tanah yang digunakan untuk beternak ikan
= 2 3
4
– 22
20
= 11 22
–
4 20
= 33
20
= 165
100
× 5
5
55 − 22
=
20
= 1,65 hektare
9. Jawaban: c
Jarak sebenarnya = 450.000 × 4 cm = 1.800.000 cm
= 18 km
10. Jawaban: b
Permasalahan perbandingan berbalik nilai.
Kecepatan Waktu
50 km/jam ⎯→ 1 1
2 jam
60 km/jam ⎯→ n jam
50
60 = n
×
1 ⇔ n =
1
2
1
50 1
2
60
11. Jawaban: d
6x + 2 = 4x – 5
⇔ 6x – 4x = –5 – 2
⇔ 2x = –7
⇔ 2x + 3 = –7 + 3 = –4
= 1 1
4 jam
100 Kunci Jawaban dan Pembahasan PR Matematika Kelas IX
12. Jawaban: b
P = {1, 3, 5, 7, 9, 11, 13, 15, 17, 19}
Q = {1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72}
Anggota persekutuan himpunan P dan Q yaitu 1,
3, dan 9.
Jadi, P ∩ Q = {1, 3, 9}.
13. Jawaban: c
R = siswa gemar renang
V = siswa gemar voli
S
R V
20 – x x 23 – x
12
50 – 12 = 20 – x + 23 – x + x
⇔ 38 = 43 – x
⇔ x = 5
n(V) = 23 – x = 23 – 5 = 18
14. Jawaban: a
3x – y = 10 × 3 9x – 3y = 30
2x + 3y = 3 × 1 2x + 3y = 3
––––––––––– +
11x = 33
⇔ x
3x – y = 10 ⇒ 9 – y = 10
–y = 1
y = –1
= 3
Nilai x – 2y = 3 – 2(–1) = 3 + 2 = 5.
15. Jawaban: c
x = harga 1 buku
y = harga 1 pensil
4x + 5y = 15.500 . . . (i)
2x + 6y = 13.000 . . . (ii)
Eliminasil x:
2 × (ii) : 4x + 12y = 26.000
(i) : 4x + 5y = 15.500
–––––––––––––––– –
7y = 10.500
⇔ y = 1.500
Substitusi y = 1.500 ke (ii):
2x + 6 × 1.500 = 13.000
⇔ 2x + 9.000 = 13.000
⇔ 2x = 4.000
⇔ x = 2.000
Harga 3 buku dan 2 pensil = 3x + 2y
= 3 × 2.000 + 2 × 1.500
= 9.000