A) 35 * 34 + 35 . 86 + 65 * 75 + 65 * 45
B) 22 + 23 + 24 +… 27 + 28
C) 1+3 + 5+ 7 +…+ 99
A) 35 * 34 + 35 . 86 + 65 * 75 + 65 * 45 B) 22 + 23 + 24 +… 27 + 28 C) 1+3 + 5+ 7 +…+ 99
By Eden
By Eden
A) 35 * 34 + 35 . 86 + 65 * 75 + 65 * 45
B) 22 + 23 + 24 +… 27 + 28
C) 1+3 + 5+ 7 +…+ 99
A) 35 * 34 + 35 . 86 + 65 * 75 + 65 * 45
= 35 (34 + 86) + 65 (75 + 45)
= 35 . 120 + 65 . 120
= 120 . (35 + 65)
= 120 . 100
= 12000
B) 22 + 23 + 24 +… 27 + 28
= [(28 – 22) : 1 + 1] . (28 +22) :2
= 7 . 50 :2
= 350 : 2
= 175
C) 1+3 + 5+ 7 +…+ 99
= [(99 – 1) : 2 +1] . ( 99+1) : 2
= 50 . 100 : 2
= 5000 : 2 = 2500
HỌC TỐT 😀