Ricarda earns a $25 allowance each week. How much allowance will she earn after 7 weeks. Explain how to use mental math to solve.

25*7=175 dollars

(1) 5*7=35, write down 5 and advance the 3

(2) 2*7=14, 14+3 (from step one) = 17 write down 7 and advance the 1

(3) since there is no more digits to do calculations, write down the 1

the answer is 175

(is this the mental math you re talking about?)